Sure.
http://www.engadget.com/2007/07/14/t...with-your-own/
It will run you appox. $30, if you can find a site that sells them.
If you are looking to save a few extra bucks, then follow this tutorial.
http://www.myspace.com/playstaion3hddmod
The sata cable is approx. $7.
I don't think getting a SATA 3.5 HDD faster than 7200 RPM will increase speed too much because of the encryption process slows things down(correct me if I'm wrong). Also, not very cost effective since raptor 10,000RPM 150GB is $170.
This HDD seems like the way to go.
http://www.newegg.com/Product/Produc...82E16822144701
So you either get a HDD extender $30, HDD Ext. enclosure $35, and SATA 250 GB 3.5 HDD $70 ($150) or just get the SATA cable $7, and HDD $70, and enclosure $35 ($120).
I'm also considering breaking open my Seagate 150GB Ext HDD. It's got an ATA IDE inside and those work as well with the proper adapter.
TP