I think I might have worked out what the problem is (and it's my own stupid fault!) :doh: I just remembered that the DG845GT is actually not officially supported by AOL (although I have been using it with AOL for 8 months with no problems). I ran some port checks last night and most of them are closed, which i guess could be caused by this incompatiobility somehow. 63392 is open, but 29339 is closed (firewall off, all ports forwarded). Only thing is I'm surprised LFS runs Ok with 29339 apparently not working.
Anyway, I'm not going to buy a new router as I'll be moving from AOL in August anyway which I hope should solve the problem.