I got ubuntu installed on the D620 yesterday night quite painlessly. The following searches on google helped me.
1. ubuntu howto Dell 1390
2. ubuntu howto nvidia
3. ubuntu howto vlc
Those are the ones from memory.
The wifi card is running of a ndiswrapper, and it works fine, unless you want wpa-psk. I haven't figured out how that would work. Oh and one X11 restart the screen goes bad. Thats probably because the driver isn't the latest nvidia driver. Plus the chip in the laptop is the Nvidia Quadro NVS 110M. I might try installing the latest drivers tonight.
By default the kernel does not have smp support. Adding the linux-image-686 fixes that, so that you make use of your core duo CPU.