I think most people believe that an SSD for your OS drive (and a few of your favorite games) along with a fast 7200 RPM HD is the ideal setup. Something like an 64-80 GB SSD along with a 1 TB WD Black Edition drive. Just think what you would have spent on two Raptors... well, subtract $100 from that for a fast conventional HD and put the rest of that money into an SSD.
Also... RAID 0 with 2 drives will double your chances of a catastrophic hard drive failure. Just something to keep in mind.
I think the investment in an SSD gives you alot more performance in return than an additional raptor. The SSD for system disk + Raptor for Games is a good setup i think. You might even put some games you use the most on the SSD.
Good SSD is Intel X25-M, try to get an intel SSD as they are really the best ones.
I've just started using an OCZ Vertex for my sys drive, and Samsung F series for my storage drive, it's proved to be an awesome combination. The SSD makes so much difference to the performance, Intel are definatly the best SSDs but also the most expensive, OCZ come a close second and are slightly more affordable. My boot time from cold to Win7 fully loaded is 31 seconds so I would definatly recommend the SSD option...
Yes, an Intel SSD boot drive for Windows and games, and move your documents, pictures, music to your regular HDD. I believe you could also move your PageFile on that HDD. So the 80 GB could be just fine or go with the 160GB.