First subscribe to the devel mailing list (see below). You have to be subscribed anyway if you plan to participate. It's rather well seen that any developer also is subscribed and answers questions in the users mailing list if no user can.
Before you can do any development you need to be familiar with SourceForge.net and have a user account there.
Important knowledge is to be familiar with Linux.
The usual way of development here is to make patches and send them to the patch tracker. This way any code change gets a chance to be discussed and revised if needed. The optimal procedure for the patch handling is:
Simple text corrections may also be sent to the mailing list but there is no guaranty it is answered and may get lost.
Bug reports are handled exactly like patches but no time frame is given.
The user mailing list can be found in the support section.
There is currently no developer mailing list, so just use the user mailing list or contact me direct.
Anonymous read access to CVS is possible through
login with password "" (empty) and check out module "FBdev" or any subdirectory.
If you only want to get a part of FBdev (i.e. a driver) just check out the appropriate subdirectory (i.e. "fbdev/radeonfb").
Directly browse the CVS repository via the web.
See support section.