Even though, I strongly recommend upgrading do Win 7.
Great idea, in addition to having a supported OS, Windows 7 has far superior memory management, unlike XP, which finds a way to use all (up to 3.25GB) that one adds.
The Dell Latitude D620 should be able to run Windows 7, as I recall, some were shipped with Vista. These drivers can be used to install Windows 7, some may require to be installed in Compatibility Mode. Some of this model are also sold on eBay & occasionally Newegg as refurbished with Windows 7 preinstalled.
Windows 7 should be a good performer on that Intel Core Duo, though depending on the graphics installed, it may be best to turn off the Aero features. It was a premium notebook in it's day, a solid business performer.
Also Linux Mint will install on it & there is Skype for Linux, plus the torrent software that you want in Transmission & it's a 100% Free choice. No drivers to configure, install it, update & go. It should run the latest versions with no issue, speaking of which Linux Mint 17 LTS (RC) 5 year support will soon ship, unlike Windows, the RC will update to the final release.
Regardless of what other software you run, it's best to get off of XP.