Yeah it's true - listen to Daniel15!
The Intel 810/815 are DirectX 7 based (or is it 6?) and definitely only go up to 24 bit (I've had machines with both 810 and 815 chipsets, poor sod that I am!). But as Daniel says you just need to make sure you switch down to 16-bit to get N64 emulation going. 845 and 915 are later versions and will have 32-bit colour.
Also, I bet you haven't got an AGP slot on your motherboard? Most of the Intel 810/815 based boards didn't come with one, which means you'd have to get a PCI card instead. These tend to be expensive (£30- £40 for a decent one) and it really isn't worth it as the performance isn't enough to warrant the cost! You could plump for a cheap Voodoo card instead from eBay - read on.....
The best plugins to use for these chipsets on either PJ64 or 1964 are -
1) Rice's latest excellent plugin (6.1.1 I think - this seems to give best compatibility)
2) Glide64 and eVoodoo (also both great)
Do NOT use Hacturux's wrapper with Glide64 as it converts the Glide calls to OpenGL - and OpenGL support on these Intel Chipsets are rubbish. eVoodoo converts to Direct3D which is better supported. OR you COULD go on eBay and pick up a Voodoo2 card for peanuts (don't pay more than £5 or $10 including shipping!) which will allow you to use Glide64 natively without eVoodoo. This will give the best performance, and will allow you to play the most games. Also, the author of Glide64, Gonetz, is still working on it to improve compatibility!
I have PJ64 running on a P3 800 with Intel 815 graphics, (my Voodoo card doesn't fit in my SFF case!) and it's perfectly acceptable - just bear in mind that not EVERY game is going to work!
Also, be prepared to lower the screen resolution a bit (remember that you can go down as low a 320x200 if need be!).
Most people these days (especially on here) have Radeons and Geforces and tend to think that there's no way that such a lowly chipset can do the job, but it just takes a bit of effort to set up - people tend to forget that Corn could run Mario64 and Zelda on a Pentium 233 and Voodoo1 card!