I just bought 2 sticks of 2GB 240-pin Crucial Ballistix (the yellow ones) from Newegg, but now I'm not so sure of their compatibility with my system.
I have an Intel i7 860 and a Giga-Byte GA-P55A-UD4P motherboard.
I thought the Ballistix memory and my motherboard were compatible because I went to the crucial site and ran their memory finding tool using the UD4P motherboard. I just noticed though that the memory sticks I bought are 1.65 volts and the motherboard memory sockets say 1.5 volts. Will this be a problem?
Also, after checking the Intel site, my particular processor says 1066/1333 RAM only. This looks like a problem too.
Don't worry at all - in terms of memory voltage, you'd be fine - the IMC on Core i7 can handle a max of 1.65V according to Intel, but really it can handle around 1.7V, but you shouldn't up the voltage if you don't need to, you can run RAM at lower voltages if you want - lower voltage is better, but only if it's stable.
As for the speed - the Core i7s only officially support 1066MHz/1333MHz RAM - it can run it at much higher speeds, many have run it at 1600MHz+, some can even run it at 2200MHz+ if they have fast enough RAM.
Look at the first qualified memory module - somewhere it says 17600 - that means PC3-17600, which is a memory rating/speed - it is 2200MHz, and I doubt that memory can run at speed on 1.5V. Also, down at the 1600MHz (PC3-12800) list, TR3X6G1600C8D is listed - it's a Corsair Dominator kit which runs at 1600MHz at 1.65V, so you really shouldn't worry. Heck I bought 1.6V PC3-16000 RAM and it's compatible with my i7 930.