I did this just last week. Downloaded Senuti, connected my PC formatted ipod to my imac 24, and followed the directions listed on the download site to copy my library. Once the library was copied onto iTunes, I used the "reset factory settings" option on my mac's iTunes, which deleted the entire library and replaced it with the library that was transferred to the mac by Senuti. In the process the iPod gets re-formatted to mac, thus allowing it to synch on the mac for automatic updates and new title additions/deletions. Thankfully everything went smoothly. If you plan on reformatting your iPod make sure you deauthorize your iTunes on the Dell first, then authorize your mac iTunes using the same username and password. If you plan on using the iPod on both computers you'll have to manage your library on the mac manually as it will not synch as it did with the pc. Good luck with your transfer.
Luis