Hi Kyle,
I was in the boat as you with my D620. Mine came with the Intel wireless card. I just bought one of the Dell Broadcom ones off Ebay, plugged it in, and worked out of the box with the retail 10.6. Just search Ebay for "dell 1390 wireless card" and make sure that it's a mini PCIe card. I picked mine up for $8 including shipping.
Note: when I upgraded to 10.6.5 the card stopped working. But, I applied the latest EDP package available on the osxlatitude website, and all was working again.
Edit: I realised that the EDP package on the website is version 1.4, but the latest on the forum is later... 1.5rc4. I haven't tried 1.5rc4 yet, but I'm not having any issues with 1.4, so I tend to work under the adage, if it ain't broke....
webbos. c|