Yes that computer will work, the built in ATI Rage and Crystal CS4236 should work fine for most DOS games.

You will run into some speed related issues with some old DOS games and also the famous Pascal compliler bug which makes some games fail to start but they can be patched.

Most games from 1992 - 1996 will run fine without any advanced tinkering.

Define 'older'.

This machine will run most DOS games from 1994-1997. There are still some speed-sensitive games from 1994-1995, though, so it's possible it may run a few games too fast from those years. And the Pentium II is not very flexible in terms of disabling cache. You can disable L1, but it slows down too much (think 286). Many games from 1993 and earlier are speed sensitive, so won't run well on this system, unless they are from 1989 and earlier (IOW, 286-era).

The integrated ATI should be fine, but if there are issues, there's lots of cheap PCI options out there. See the PCI benchmark link in my signature.

I would recommend for sound an Audician 32 Plus ISA card. It's very popular on these boards due to good sound quality and high compatibility. Just search 'audician 32 plus' on ebay. They are about $20-25 shipped. If you want general MIDI music, then a DreamBlaster S1 or X2 would work awesome on the Audician's wavetable header.

If you already have it, just try it out!
P2 makes a great late dos gamming PC, and if your lucky the earlier ones wont be affected by speed issues but only testing will confirm.