In Win9x, click Start->Run and enter "msconfig". In the msconfig utility, you should see a startup tab where you can specify which programs should load when you start your computer. Get rid of all the junk!
In Windows 2000/XP, right click on My Computer and choose "Manage". When the Computer Management console comes up, choose System Tools->System Information->Software Environment->Startup Programs from the treeview on the left. This will show you all the programs that are set to run on startup. To remove some of them, you must edit the "Startup" folders for the current user, the default user, and All Users. This can be done by right clicking on the Task Bar, selecting Properties, then Advanced->Advanced... To remove others, you must edit the following registry keys:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
Be careful when editing the registry. Make sure you look each program up before disabling it.
Finally, on Win2k/XP, you can also modify the system services. A service is a program that runs without a user context, like IIS (web server), FTP Publishing, etc. Again, bring up the Computer Management console and this time choose Services and Applications->Services. You only need to disable services that are unnecessary and marked "Running". To disable a service, double click it and change its startup type to "disabled". Potential services to get rid of would be DHCP Client (Depending on your ISP configuration), Fax Service, FTP Publishing Service, IIS Admin Service, Internet Connection Sharing, SMTP, Telnet, Word Wide Web Publishing Service (IIS). Note, disabling services will not cause clients to malfunction. For instance, disabling FTP Publishing doesn't mean that you can't FTP to other sites, it means that people can't FTP to you. In other words, these are mostly "server" applications. I should point out, however, that many programs rely on these services. For instance, if you create Web pages with Macromedia Dreamweaver, you definately don't want to disable IIS on your system! If you don't have a public IP address for your internet connnection, you don't want to disable DHCP client! And so on..... look things up before you tear em down!
P.S. you'll need to do all of the above via an account with admin priviledges.
Slackmaster 2000