First I assume you are using Windows 7 X-64. I've posted on this site before that some LAN cards (usually On Board LAN) won't work with Windows 7 x-64 whatever drivers
are downloade even if Windows says latest driver
is downloaded and working.
This is actually because the hardware is still only 32 bit. Typical cards that have this problem are the Via Velocity Family Gigabit cards.
Device manager reports these as working but you will see a yellow exclamation mark with Unidentified network.
The simplest solution (even on a desktop) is to use a USB===>LAN connector -- very cheap and fast -- machines usually have enough USB ports these days.
Here's a picture of such a device -- costs around 10 GBP (tax paid) in the UK but you could probably source one cheaper.
These ALL work with ANY version of Windows 7 and do save all the hassle.
Here's a pic of the device.