Dazza-E-, Ok glad to hear your player is running again. There is some debate as to if 4GB chiPod's actually exist. Most have much smaller chips that have been hacked so that they read as 4GB memory chips. Formatting removes the hack and reveals the true size of the chip. FAT32 seems to be part of the hack. The only way to find out your true chip capacity is to note it's brand (Samsung or Hynix etc) and the part number then do a Google with this info you should be able to find specification info.
Here is a post that explains th e situation
http://www.mympxplayer.com/viewtopic.php?t=424
You are lucky in one way some 4GB players have ended up being 128 or 256 MB chips.
Anyway glad you are up and running. If you want to theme your firmware find a theme you want and load the images using s1res into your own firmware dump.bin
Here is a tutorial on how to do it.
http://www.mympxplayer.com/viewtopic.php?t=206