This guide is nearly a decade old, and mostly a decade out-of-date. While it does allow you to run Day of the Tentacle, a DOS game, on Windows XP, it's a bit complicated. I strongly recommend anyone trying to run DOTT on a modern Windows install, or on Linux or MacOS-X, to use ScummVM instead.
You can find the original CD for DOTT in second-hand stores, and Lucasarts has released it on CD and (I believe) on DVD-ROM - but in all cases they've not updated it to run on Windows, and it generally needs some coaxing to work properly. These instructions show how to do this on Windows XP, but should (I've not tested) also apply to Windows2000.
Windows XP does a pretty good job of emulating a ten-year old DOS platform, at least as far as gameplay and graphics go, but it doesn't do a good job emulating the antique sound hardware of that era. Luckily Vlad Romascanu was written the excellent VDMSound system, which emulates the SoundBlaster and MIDI hardware that DOTT needs.
After this, your c:\dott.cd directory should look like:
In the screenshot below, VDMSound is installed in its default directory and the CD-ROM is the F: drive:
There is one solution, but it's a bit of a hack. You can copy the entire DOTT directory, and the DOTT.EXE file as well, to the local drive (in my case, to the C:\DOTT.CD directory). After this, the C:\DOTT.CD directory looks like this:
In the above case I've made a second shortcut (Day_of_the_tentacle_local) to run this local DOTT.EXE executable, and with D:\DOTT.CD as the current directory. The shortcut's properties look something like this:
Savegames are stored in the C:\DOTT.CD\DOTT directory. The only downside is that the entire contents of the CD are now on a local drive (that's around 270 megabytes).