Check the linux hardware database (link from euglug.org's links page) to
see what cards are compatible... 3com are the most popularkly supported
afaik (I've been using kernel modules 3c59x and 3c9xx if I remember
rightly, and the only problem I've had is in trying to use the wrong one,
ie, forgetting which card I've got!)
Networking is fully supported in linux, there is no "special" support for
cable/dsl users (or is there/why??), unless you're talking about doing
fancier networking like doing appletalk/ipx/802.11b, which are also
supported. I'm on UOnet, so I cannot make suggestions are to
cable-vs-dsl, or even tell you where to live to get service...
I have heard bad things about emachines though, just that they rank really
low in system performance metrics b/c of cheap parts, but most I've seen
do work. Be advised to turn off default system services when using
redhat! This should not be a concern, however, if you use the common
hardware firewall when setting up your home net... you'd just be insecure
on the inside, which is usu fine.
good luck!
ben