There are different speeds.
1. The speed shown by the connection icon in the taskbar in Windows XP (like: 54 Mbps) for a wireless connection..
2. The speed (in MBps) it takes to copy a file in your home network from one PC to another PC. For example: a 100 MB files takes 15 seconds to copy. If both PC's are connected via an Ethernet-cable it's faster than if one or both are wireless.
3. The connection speed (upload and download) shown by a speedtest on Internet (using a PC connected via Ethernet). That's limited by the speed of your ADSL connection with the ISP. If that's much slower than what you pay for, contact their customer service. It could be a setting in your modem that needs to be changed. They should know the details for all modems they support..

Kees