Yes, it has a built-in NIC card, aka wireless card.
You first should have a wireless router. If you have a laptop, try connection that to test the connection.
Then, if you haven't messed with the router configuration, I assume you do not have any security. If you do have any security, then you would have to access your router configuration, find what your passkey is and what kind of security you have.
Step-by-step:
1. Start-->Settings-->"Connections" tab-->Dell WLAN Utility
2. Press the big "Turn On" button :)
3. A window should pop up and say "New Network Detected"
4. You should select the "Work" option
5. Press "Connect"
6. If asked for your passkey, input it
7. If successful, you should see green bars in the lower right-hand corner
8. Use Pocket Internet Explorers to browse
OR refer to Ikehiker's awesome wi-fi guide for easier instructions WITH pictures:
http://wifi.aximsite.com/wifi_net.html
Specific instructions for x51v running WM5:
http://wifi.aximsite.com/wm5.html