The one thing you don't mention is the size of the SSD you will be possibly purchasing. I'm going to assume something over a hundred GB. In that case I would just use the SSD as your primary drive for obvious things like your Operating system and for programs. Then just use the 500 GB HD as storage like photos and music. No RAID is necessary.
- What size is the SSD
- What make/model is the SSD, this is very important
- 6gbps SATA is not neccesarily required for a lot of SSD's at the moment, do not buy just based on "it is 6gbps sata" this is the speed of the bus and not the actual speed of the drive
- no raid req as you have 2 completely different disks, if you added a second 500gb matched drive in there I would configure the 2x500gb in RAID0 for fast secondary storage (pro setup and worthwhile)
Unless you are blowing huge cash on the SSD you are going to need to use something like symbolic links to keep as much data off the SSD as possible to maximise space
Having itunes use music from the 500gb is easy, store music on 500, drag into itunes, job done, something to consider is how much crap itunes stores in your appdata totally eating at your ssd's space - use symbolic links to move this crap onto the 500gb
If you use steam, steam only allows game files to be stored in the main steam DIR - symbolic links to move the older games/games you don't want on SSD onto the secondary 500gb storage
My storage setup is
OCZ Vertex 2E 120GB ssd
2x640gb WD 64mb cache sata drives = 1.2TB RAID0
2x1.5T raid1 for mirrored slow storage
I find this setup to be pretty damn fast, secondary storage as RAID0 is sick for browsing through huge DIR's of large files, details of the files loads so damn quick
Don't use raid because your slower drive would slow down the SSD. Have you seen the youtube videos on the hybrid drives? They are mechanical drives with 4 GB or onboard ram (ssd) and it works just a tad bit slower than a solid state drive but is so much cheaper.
Amazon.com right now has a 500GB Hybrid Drive for $98. The great thing about hybrids are that they remember which programs you use the most and move it to the ram so the programs you run the most run as SSD speeds.