no problem , you can Secure your linksys router wrt54g using WPA and WEP
Click the Wireless Security sub-menu option at the top of the page. This is where we will provide the most important security setting.
Next to Security Mode, select WPA Personal from the drop-down list.(If you have trouble connecting to your linksys wrt54g connection, you can try selecting “WEP”, but your connection will be much less secure)
Next to WPA Algorithm, select AES. If you have trouble connecting to your wireless router, select TKIP.
Specify a long WPA Shared Key with a mix of upper and lower case letters, numbers and punctuation.you must get very creative.
Make sure you write down this key somewhere, You will need this information when you connect to your linksys Wrt54g.
Click the Save Settings button .