I have an iTalk and iPod as well, and to answer your question -- no way to improve the recording quality that I know of.
iTalk is marketed as a voice recorder, and for that purpose, 8 kHz is fine.
That's not to say I wouldn't welcome hi-fi iTalk recording (I would). What I have heard is that Apple's hands are tied by the recording industry. The RIAA doesn't want people taking iPods to concerts and making hi-fi recordings of their artists. Or so the story goes...
well it's kinda sad ,actually my only purpose is to record some tv shows in decent quality ,that can be listen to ,while im in the car because it sounds pretty lame when i record a cnn program or whatever