depending on your budget en all. but if your only connecting a modem to it. the cheapo lan cards will suffice (cost a few £ tops) no need to splash out on a 10/100/1000. I'm not a big fan of routers myself but then thats just me!
Edit- bargain!
http://www.ebuyer.com/customer/produ...duct_uid=42061
since you'll be using 10mbit tops cpu usage will be negligable