Right now i have a gaming laptop with two 320 gig hard drives one for the OS/program files and the other for videos and music and stuff like that. It works out fine this way except that i have far more program files than other files so one hard drive is over half full while the other has a lot of free space so a friend recommended that i configure RAID 0 or stripe them so that windows only saw one 640 drive and he also said it would run faster (windows could write to both drives at once). Does anyone with experience in RAID know if it is significantly faster or what the advantages or disadvantages are?

Yes, it would be faster. Not twice as fast, but noticeably faster. But, there are a few things you should know before you go RAIDing it up.
First, RAID 0 NEEDS all of the HDs that are part of the array. If even one is missing or goes bad, then all of your data is unusable. Secondly, I don't think that you can make a RAID array without formatting the drives, but I could be wrong about this so correct me at will.

Hyperkultra got the speed and the reliability pretty much exactly correct.

Raid 0 at home conditions is not really recommended, unless you backup your data pretty much daily.

You might want to go solid state if you want reliability and have the monies.

I think Hyperkultra was right about needing to format the HDs so I've been scoping out getting an external drive to move my stuff to in order to configure the RAID and also to back it up because i am pretty aware of the risks. And concerning the SSDs, I've seen some of those but it seems like for the price its probably cheaper just to get and external and back up religiously. I had also heard that because SSDs use flash memory they are only good for a certain amount of reads and writes making them not so practical for running an OS on.

Anyway thanks for the feedback and by the way, does anyone have a good external hard drive manufacturer that they'd recommend besides the basic Seagate or WD?

While SSDs are limited in a technical sense to a certain number of read/write operations, Windows 7 actually detects that it's installed on a solid-state drive and manages the file system in a different (more efficient) way. The biggest problem people had with SSDs in older computer setups was that their file systems would try to format the SSD to move all the data "closer" to the nonexistent read/write head. Since flash memory can access all of its contents at the same speed, there's no need to "defragment" a solid state drive.

SSDs as boot/OS hard disks is a pretty well established practice; the SSD is as likely to survive several years of operation as a standard hard drive is to die from some error or another.