When installing Win98 SE on any PC, it's 99% likely to install absolutely fine.
However, you will almost always need the driver files for your graphics, sound, modem, USB (maybe) and other little bits and pieces that are inside that might not accept Windows 98's default drivers.
To get the drivers, try going to Compaq's web site or Driverguide.com ...... or get hold of the original driver CDs!! You can blag your way through it sometimes depending on exactly what hardware is inside the Compaq but that's only with years of experience that I wouldn't be able to explain over the Internet without seeing the system!
Hope I've pointed you in the right direction
DJNafey
IT Manager and system builder