2 gigs is the max.
I couldn't find specs so I bought a Sandisk 4GB Extreme III Compact Flash. Unfortunately, I found out the max capacity is 2 gig. The slot would only recognize 2 gigs worth of music. The 4 gig works but will not account for the 2 extra gig worth of music. So I only posted 2 gigs of music on the 4 gig compact flash card so I could control which songs were readable.
Just get a 2 gig compact flash card. They are really cheap now. Under 40 bucks if you look for specials.

- Kevin