I can help for download rtm 875t-587 lan driver supportable for windows xp.

You will need to open up your network connections click start control panel network connections this may vary depending on your operating system look for local area connection if you see a red x or a yellow exclamation or question mark you will need to update or install the driver or it could be firewalled
If you are trying to connect through a modem/router the driver should have come with a disc provided by your ISP internet service provider or your motherboard disc
you might have to connect the usb lead to your modem to get a connection then
click start control panel administrive tools computer management device manager scroll to network adapters should see a yellow question mark? right click install drivers if you cant find the driver hopefully one of these will help you
http://download.cnet.com/%7Bvalue=http://www.download.com/802-11b-g-atheros/3000-2112_4-162108.html

http://alpha.majorgeeks.com/Intel_Network_Adapter_Driver_for_Windows_7_d6273.html

http://majorgeeks.com/SiS191_Gigabit_LAN_&_SiS190_LAN_Driver_d5923.html

http://majorgeeks.com/IntelR_PROWireless_LAN_2100_Network_Connection_d4598.html Latest

http://majorgeeks.com/downloadget.php?id=5240&file=15&evp=5fbb1c6e47482358c61a5236fb38a112
VIA LAN Driver. If you don