I'm using a shitload of VST's in Renoise on the album I'm working on currently and I can't play anything back without it stopping the sound engine because it's using 100% cpu on my soundcard. Disabling it is useless because all I get then is noise.
Which is exceptionally a bad thing in this case.

I'm clueless about external cards. Doesn't need to be anything fancy with lots of extras. Just something simple but powerful.

What you mean by "100% cpu on my soundcard" ? Because soundcards don't have cpus Are you sure vsts aren't maxing your computer's cpu?

Hmm, yeah.. I just realized. I guess I just need a better pc. I assumed a sound card also had some kind of processor like a video card.

You could always trying freezing a few midi tracks or exporting some tracks that are static. Then you won't need to run those VSTs in realtime as its just a WAV. Its a pain (and time consuming!), but will get you of trouble while you sort out a more powerful pc.

Or just use less VSTs.