Tutorials you can get

One day, I'll sit down and write a Power User's Guide to Windows. Until then, try

Fun

Although Microsoft is quite keen to stress that all Windows versions currently look and feel pretty similar, deep down, you must already know that there are some architectural changes or even some user interface differences. Like I was installing a Dynalink USB Webcam driver and the manufacturer's install script (.inf) had an older version of TWAIN .dlls compared to what was in Windows ME and Windows 2000.

Windows ME asked me "The target file is newer than the file we are trying to install, do you want to copy over the target file, - default answer No".

Windows 2000 asked me "The target file is newer than the file we are trying to install, do you want to keep the target file, default answer Yes". Or was it No?

Hilarious.

The Legacy Application

We don't talk much about CPM/80 nowadays, but things like Wordstar 3.3, dBase II, Multiplan, were the legacy apps which had to be re-compiled, I suppose to support MS-DOS.

Then we have MS-DOS apps. Generic ones (a.k.a. "well behaved") would still work when we migrated to Windows '95 - FAT16, without re-compiling. What MS-DOS apps have problems in Windows 3.x - FAT16? Those that:

write to video card memory. (usually games, but also some charting/graphics programs, screen capture programs)
handle direct communication to keyboard, serial port or printer port. (usually games, but also some terminal emulation programs, printer utilities)
handle direct disk i/o, bypassing MS-DOS services (usually disk repair or management utilities, backup utilities, device driver hooks in CONFIG.SYS)
use special memory access schemes A General Tutorial on the Various Forms of Memory

Then we have Windows 3.x to Win'95 migration. Apps that fail:

cannot handle long file names - (minor problem)
cannot handle long path names - e.g. Norton Backup, MS Backup/DOS Backup
cannot work with Win'95 virtualised disk access (need to slow down Win'95 by using DOS mode disk access). Usually some disk drivers.
cannot handle larger hard disks
assume that there is no Taskbar/Start Menu and want to take the whole screen.
depend on Win'3x device drivers.
assume a 16 bit colour screen driver and cannot handle the richer colours in Win'95 or the change in device drivers.
Virus Scanners

Then we have Win'95 - FAT16 to Win'95 (or later) FAT32. Those apps that have problems are:

apps that assume a FAT16 structure - usually Hibernation, Save State Power Management utils for Notebooks, Borland BDE (database engine), Disk Utilities.

Then we have Win'95 to Win'98 migration. The most common problems arise from:

Hardware that is APM power managed when Win'98 / Win'ME are ACPI power managed causes problems.
Some differences in device driver specification

Then we have Win'9x migration to Windows ME. Apps that have these problems are:

device drivers that are written to the older specification while Windows ME and Windows NT/2000 use the WDM - Windows Driver Model. Typically, these include scanners, digital camera and capture board drivers, disk drivers, proprietary CD-ROM drivers, specialised SCSI drivers.
those that insist on copying their versions of .dlls to \windows or \windows\system.

Then we have migration from Win'9x to Windows NT4. Problems arise when

apps cannot handle NTFS.
apps that i/o to disk using legacy DOS services or Win'9x services
apps that use some standard Win'95 specific .dlls - a.k.a. Common dialogs, File dialogs, 3d effects for dialogs. e.g. Corel WordPerfect Suites dedicated to Win'9x, InfoCentral.
apps that need intimate DirectX access (NT does not support the latest DirectX drivers)
apps that need Win'95 Video states / access. e.g. Lotus ScreenCam.
apps or drivers are not able to work with Windows NT Driver Model. - Scanners, Video Capture Cards, Win'95 SCSI drivers.
print redirection drivers (e.g. Envoy).
disk drivers for CD-ROM, external disks, backup utilities
apps that assume that the Win'95 registry
USB is not supported in Windows NT4
Virus Scanners

Then we have migration from Windows NT4 to Windows 2000. Problems arise when

Hardware does not work with the enhanced ACPI power management in Windows 2000 (motherboard BIOS and disk drivers)
Device drivers
Virus Scanners

Working with several Microsoft OSes

Multi-Booting

Partitioning Primer - The Partition Manager FAQ

Virtual PCs

VmWare

Get another PC!

Troubleshooting Win'95

Setup Problems

Switch off or kill your Virus Scanner. Also see Windows 95-98 Setup Error Message List

Start Up Problems

For background, read Troubleshooting Windows 95 Startup Problems and Error Messages. To find out whether any startup programs are causing problems, disable them and then re-enable them one by one. Win'98 has a Startup Manager but Braw Stower's Startup Manager is a long time fav and free.

You may get the message: Cannot Find a Device File That May Be Needed..

Once up, you want to know How to Troubleshoot Registry Errors

Or you may need to do SCSI Setup & Basic SCSI Troubleshooting in Windows

Sometimes you can start up but the screen looks dreadful. See:

Q127139 Troubleshooting Video Problems in Windows 95
Q124267 (Display Adapter Information and Useful Switches)

Application and Windows Performance / Crashes

If Windows is slow, there could be many reasons. Some of them are disk access related:

You may have "DLL Hell"

Once you have a preferred DLL version, you may not be able to replace the "bad" one on your PC:

Rarely do you need to know How to Troubleshoot Windows Internal Stack Overflow Errors.

If you cannot "see" other computers in the network, see How to Check Network Connectivity Using Net Diagnostics. You may need to know How to Uninstall Novell's 32-Bit Network Client

If you have a new Window Game, and the screen looks dreadful or you are unable to run the game, see Microsoft DirectX 6 (Home User) Troubleshooter or Microsoft DirectX Support Center

Shut Down (or refusal to)

Miscellaneous Windows '9x Knowledgebase Tips

How to Set Up a Network Printer Using Point and Print