How can I check under linux or windows if my ethernet card is starting die? , I mean everything seems to work fine with the lan, but things are a bit slower... what software, or hardware do I need for this?[cable/ethernet card tester of something].

Since today my terminal server was really slow, [this was starting 4 days ago, getting slower and slower], and I just switched the ethernet card [RTL8139D] and now everything is fast again [the entire computer was slower because of this, it ate cpu, 100%-80%...].

Can anyone reccomend me some tools[better], software ? [that works with linux and windows]

Robert B