I have noticed with some Linksys Network cards mainly the NC100v2. Windows XP original version has native drivers for that card. And they work great until you upgrade to WinXP SP1 or SP2. Then every time you restart your system it will not get a DHCP IP address, or if you have a Static IP address set. It will not attach to the network until you Disable and ReEnable the LAN connection from Control Panel.

Looking at the Linksys website you can download drivers but, there are no drivers for Windows XP. I found a fix for this issue, you just need to force WinXP to use the Windows 2000 driver. To do this and correct the issue.

First download the drivers for the Linksys NC100 10/100Mbps Ethernet Card from the Linksys website: http://support.linksys.com
Then run the downloaded file, extract the files to the default folder: c:\nc100v2

Go to START > (right click) My Computer > (click) Properties > (click) Hardware tab > (click) Device Manager.

Once in the Device Manager > (click) The plus symbol next to the Network Adapters category > (double click) Network Everywhere Fast Ethernet Adapter(NC100v2) > (click) Driver tab > (click) Update Driver > (check) Install from a list or Specific Location(Advanced) > (click) Next > (click) Don't search I will choose the driver to install > (click) Next > (click) Have Disk > (click) Browse.

Then Browse to this folder: C:\nc100v2\WIN2000

Then (click) OK > (click) Next > (click) Continue Anyway > (click) Finish once it is done installing the drivers. Then restart you system and it should be fixed.