According to the specs for this router that I can find, the WAN port is 10-BaseT and therefore capable of 10 Mbps max. A replacement would be a good idea. I have a Linksys WRT54GS which has a 100BASE-TX WAN port capable of 100 Mbps and would recommend it without hesitation.
your router:-
http://www.speedguide.net/read_reviews.php?id=183
Further investigation reveals that the latest model does indeed have a 100BAS-TX WAN port so I guess you need to check the version number.