How do you change a non name brand PC with Windows XP into a wireless client or access point?

Any Windows XP PC can become a Wi-Fi client by adding an 802.11 wireless network adapter. For desktops, the most convenient after-market solution is an 802.11 USB adapter. For older laptops, the most convenient after-market solution is an 802.11 PC card. Newer laptops and handhelds may be augmented using other kinds of adapters -- for example, a PDA 802.11 SDIO card or a laptop 802.11 ExpressCard. However, most new laptops already have a factory-installed internal 802.11 wireless adapter (mini-PCI card). If you're not sure about your own Windows PC's capabilities, check the Network Connections list or the Computer/Hardware properties page. Once you install and enable your wireless network adapter, you can control wireless connections using the Wireless Zero Configuration (WZC) service built into every version of Windows XP. To learn more about installing and using Windows XP wireless clients, read this Microsoft article.

Turning a Windows XP PC into a Wi-Fi access point is a bit harder, but not rocket science. For starters, you'll need a wireless network adapter that works with a software AP program. Assuming that you want to continue running Windows XP, the most convenient solution is probably a four-in-one USB adapter like the Zyxel AG-220. An adapter like this can be used as a wireless client, or it can be switched into AP mode, using the accompanying program to manage AP settings and monitor client connections. Next, you'll need to bridge or route wireless client traffic onto an upstream network, your LAN or perhaps a shared Internet connection. Windows XP provides built-in support for both. For example, just follow XP instructions to enable Internet Connection Sharing (ICS) between the adapter used by the soft AP and a second (Ethernet or wireless) network adapter on your PC. After these simple steps, your XP PC can provide basic wireless AP or router services to other nearby wireless clients. However, your soft AP will probably not be as reliable or capable as an off-the-shelf hardware AP; it just isn't designed to focus on that task.