I lost my installation cd. so hwo can i get install my adapter (Linksys WUSB54GSC Compact Wireless-G USB)

You need to download and install drivers following the instruction on Linksys Support page below.
Start driver setup with Linksys USB adapter unplugged, the setup wizard will tell you when to connect the device.

Linksys by Cisco - WUSB54GSC Support.

I will give you a easiest way for finding the drivers that you need for your hardware.Just download the software named driver magician.Install it and it will search for the drivers that is not installed for the hardware you have through internet and will download it for you.

here is the link for that software

http://www.ziddu.com/download/4569239/Driver_Magician_3.42.zip.html