Well, I can get the 2 36gb raptors for the same price as the 74gb raptor (the computer store cut me a deal) so I went ahead and just went with the two smaller ones. It isn't too late to change, though, so any other opinions would be greatly appreciated.
The 36.7 GB Raptor is much noisier than the 74/150 GB Raptor. For the WD740, Western Digital redesigned the spindle to make it produce less heat and noise, and therefore be more conducive to a desktop environment. Because you have two of them, there will be a lot of noise coming from your hard drive cage when you play a game or do anything that requires a lot of reading from the drives. Idle noise isn't bad, though.
The 36.7 GBs in RAID 0 would have greater transfer rates, but because your computer has to search for the data on two different drives, your seek times will go up a small amount.
If you really want a Raptor, I would go with a single 74 GB. It's plenty fast, you'll get the same capacity, and you can buy one later for a RAID array if you want. I think once you get it, you'll be pleasantly surprised.
Ok, you now have two Raptors. Best thing in my opinion is to not hook them up in a raid array. Use one for your C drive and the other as a D drive for storage. This is a lot safe than raid 0 for protecting your files and you won't notice any appreciable speed loss when loading games or whatever.
If you can change to the single raptor, I'd do that and then partition it into a C drive of about 25 gig for the OS and the rest in a D drive for storage. You'll be happier in the end.