The biggest question you need to ask your self is whether you are looking for a performance boost, data protection, or a combination of both. I assume by the way that you posted your original question that you are looking primarily for data protection (redundancy).
You will achieve this by using the RAID. I currently have a PC utilizing many forms of RAID. I have my two OS drives (300GB x 2 Velociraptors) in RAID 0 for performance. I have a media volume (1TB x 2 WD Black) in RAID 0 for media performance. I have a records volume (1TB x 2 WD Black) in RAID 1 for my records and data, and I have an external RAID enclosure in (1TB x 4 WD Cav Green) in RAID 10 to hold raw video. The RAID application you choose should be determined by what you plan on placing on it.
Generally speaking, operating systems, and program files are best suited on a RAID 0 volume because this maximizes I/O rate and gives you better performance, however, since the files are spread across two drives, you have twice the likelihood of disk failure causing data loss. With an OS and Program files, this simply means replacing a disk and reinstalling. With RAID 1 you get to use all of your storage space (500GB x2 = 1TB storage), and take advantage of the performance gain.
As far as records, pictures, and any kind of one off media, you most likely want to utilize RAID 1, since this almost eliminates you chances of data loss from disk failure. The downside to RAID 1 is that you put in 2 and get 1 back, meaning that two 500 GB HD's would normally give you 1 TB of storage space, but since you are creating a mirror of your original drive with the second, that additional space is unavailable. On the bright side, when a drive fails, most RAID controllers will automatically restore the mirror image when you replace the bad disk, and your data is safe.
To get the best of both worlds, such as my external RAID 10 array, you can store data with the speed advantage of RAID 0, and still retain the "mirror" effect of RAID 1, however, this can get expensive since it requires more HD's. My video volume requires high speed access for editing, but also houses original video that needs to be secure. This also utilizes an external housing with a hardware RAID card and dedicated PCIe card to make it really fast.
The first thing you need to identify is if your motherboard will support RAID. RAID will be the best way to keep your data backed up, however, in most cases, both hard drives need to be the same capacity and recommend same manufacturer and model. It sounds like you may already have a couple drives you wanted to use, at at best case, you would only be able to utilize the smallest capacity of the two, but I would recommend purchasing a second 500 GB drive, run those two in RAID 1, and use the 10k RPM drive as your OS drive, I am guessing this is going to be a Raptor or something.
As far as RAID not being good for gaming, I am not a gamer, but with reference to RAID 1, again there is no performance gain, however, with RAID 0 you effectively double your HD read/write speed, so my guess is that it would be great for gaming.