Interesting you mention this, as I was having issues as well. I've got a Linksys 802.11n wireless router, and the 1510 card.
What I wound up doing was (and I'm forgetting what it's called) basically the WPA2 setup. It generates a code, you plug it in, and ultimately it winds up being WPA2 secured. I haven't had even the tiniest bit of problems since, and that's using Vista, Windows 7 and OS X on a variety of different machines.
I hated doing it, but I was amazed that it corrected it.
EDIT: For the record, I have had issues with Linksys routers in the past. I've got through several WRT54G's due to stability issues, both with stock and DD-WRT loaded on them.