Perhaps it's just paranoia on my part, but I envisioned some [self censored] posting a message that mimics a uuencoded set of messages.
Anyhoo, I've pretty much got it all figured out how to deal with this crap correctly. For multipart messages, the program does the following:
Basically, an entire newsgroup is processed. The "one part" messages are encoded while multiparts are saved to a temp directory. Once the entire group is processed, it goes in the temp directory, finds all parts for a file and sorts them, creates the single part file and decodes it if all the files are present. (If you don't have all the files, it'll just leave them in case you get the rest later.)
What I'm eventually hoping for is two things:
Fetching news at intervals (like every half hour) and temp files that are only stored for a set period. That way, you have x amount of time for the complete set to arrive before it removes the files.
Oh yeah.. And I suppose a gui/prefs at some point would help too. :-)
(And to think.. I'm only doing this because I'm too cheap/can't afford a similar program on the PC. ;-))