Depends all on if there is a real difference in speed in your system between the SATA and IDE drives. You could test this with a benchmark tool like HDTach or something.
Anyway, for me, I have a RAID 0 stripe with 2 IDE drives. I use it for my main OS, swap, prog files, etc. I have a secondary 120g drive for storage of data I don't use a lot.
In your setup, the SATA "should" be faster, so use that for the OS, swap, prog files, etc. All your stuff that gets accessed a lot. Then use the slower drive for data storage. Unless if you are doing some major media work, dvd, images, etc. In that case you'd want your data on a fast drive so that you can access the files faster when you need to.