Which hard drive is better:

500 GB (7200rpm) Serial ATA Hard Drive with 8MB DataBurst

Raid means data is written to each drive in turn but being raid you will only see the drives as one letter, bit of a bugger if one drives goes down unless you have a raid controller with parity information. Raid is quicker writing and reading from IIRC though.

Seagate now do a Barracuda 750GB for just

Two drives in RAID0 means it's gonna be slightly faster BUT if EITHER drive fails you'll loose the lot.

Some RAID drivers are better than others.

Also, more heat (two drives) and power consumption (ditto).

Single 500G drive gets my vote, it will probably be cheaper as well.

The newest Seagate drives are excellent performers

RAID 0 Will at the very least half your expected lifespan as you have two drives to go down.

If either drive has an error you will have lost all of the data on both drives.

Personally I wouldn't RAID 0 unles syou have a really good back up plan.

Seagate now do a Barracuda 750GB for just

Seagate now do a Barracuda 750GB for just £275.00, I actually think that is really reasonable

Yes, but you can get 360GB drives for about £65 each from the segate family, so that puts the price per gig into perspective.

IMHO if you want decent value for money you should go for two drives, just don't bother raiding them into a single drive. Nothing wrong with having two drives, each with their own drive letter.