To expand a bit on the questions of PDA virus/worms and trojans, almost anything that connects to the internet or that is capable of opening attachments is capable of carrying malware. In fact anything that is capable of carrying files or data is capable of carrying malware.
Even if it doesn't have the actual capabilities of running the malware, it can infect the base system when later connected to it. (thats supposing that you use a docking station or some other means to syncronize the files between your base system and PDA).