If it's really old i would just buy i newer one, or upgrade to a little better computer, if you are intending on using it for the internet. Otherwise your probaly gonna experience more head aches and frustration fiddling around with older comps and modems. Especially online
Now a days it's almost mandatory that you use at least a 56k modem (most people can't even stand dial up anymore) and at least a 600mghz processor or higher at least. <<<But thats just my opinion.