I've got 8GB of RAM in my Late 2008 MBP (MacBookPro5,1)

http://blog.macsales.com/9102-secret-firmware-lets-late-08-m...

Looks like this won't fly in the Early 2008 MBP, but you might be able to get 6GB in there (note "Standard RAM"):

http://www.everymac.com/systems/apple/macbook_pro/specs/macb...

For many models, the Apple supported number and the real number is different. Usually it happens when the machine supports an odd amount of RAM (like 3GB or 6GB) that would require some wasted RAM if you wanted exact pairing.

With the MBPs sold in 2008, all of them support 6GB even though Apple claims only 4GB. Go ahead and try it. If it doesn't work I'll pay for your RAM upgrade.

... and 6GB is worth it over 4GB I can tell you.