What CPU and HD storage does it have?

I ran Ubuntu on a Dell laptop with a 2.1Ghz CPU and 640Mb of RAM, a RAM
upgrade of just 512Mb would get you to that spec. I'd be concerned over HD
space an CPU speed.

RAM is cheap, as are hard disks if needed. So you'll need to get together a
list of hardware devices on the system, modems, Ethernet cards, etc...
Especially your video card, as that is going to be a killer pain in the ass
if there are no drivers for it.

Depending on the motherboard, it might be possible to add RAM. Like all
electronics equipment, there might be problems with aged parts,
electrolytic capacitors are the worst offenders. I am running an old
486dx66 computer for my router so you might get lucky.

I wouldn't sink any money into the machine it's self other than the cost
of CDs. I would go to distrowatch.com and burn a bunch of distros to
try on the machine and have some fun with it. Unless you can get RAM
for it for cheap or for free, I wouldn't be looking to get additional RAM.

You need minimum 256M RAM for ubuntu, try Puppy 4.0 for old PC.

If the CPU is 1ghz it would be worth upgrading the RAM to 512mb. I use
ubuntu 7.10 (haven't tried 8.04 on that machine i'm just waiting for
Ibex) on a Compaq P3 and it's fine.

If the CPU is 500mb or such forget i'd say. Unless you want to run
Xubuntu for a while.

I use Ubuntu 6.06 on an 800MHz Celeron (going to upgrade some day),
and Xubuntu 8.04 on an 800MHz Celeron in a laptop. Both do have 256M
of RAM. Performance is adequate, but nothing to brag about. (my
primary machine is at 3GHz and 2G of RAM BTW)

I also have Xubuntu 8.04 running on a 450MHz AMD K6-2 with 256M of
RAM. Performance is a little slower, but it does work if you have
patience. I don't know if an Intel chip in the same speed range would
do as well, back in the day, I seem to remenber that AMD had a
signifigant performance per MHz reputation,