A friend of mine just bought a new computer with integrated graphics. I don't think the computing power is as much a problem as the fact that the card takes its memory from the RAM. If you're running Windows XP, you want 512MB, and that's without something like an integrated graphics card sucking away 64MB. If you have extra RAM though, it might make little or no difference. Either way, you can get decent graphics cards for $50 that will take the load off the rest of your system (I'd go higher if you play games though). Check
www.newegg.com for video cards.
The other consideration is how it affects your monitor. This doesn't matter if you have an LCD, only if you're using a standard CRT monitor where the refresh rate is important. Crappy integrated graphics chips might not get you as high a resolution and refresh rate as you want, so check to see how high you can go. A lot of people like 1600x1200 for 4 (or more) tabling, but I prefer to keep it at 1280x1024 at 85 hz. If you start playing around with this, just take one wraning to heart: DON'T set the refresh rate as high as it can go. Yes it can still technically run, but it might also damage the monitor. Choose a refresh rate one below the max, which will hopefully be at least 75 hz.