The Linksys adapter you lost the CD for......you can simply look at the model and go on linksys.com and get the insturction and driver. Buying a new wireless adapter probably won't help you out, what you need is a good repeater/extender that can be plug downstair or whereever you want to help amplify your wireless signal.
You don't need the CD to setup your router, it's painlessly easy. Here's the step.
On a computer that is working and have access to the Internet, do the following to get into your router's configuration:
Go to Start>Run, and type CMD
You are at the command prompt, type the command ipconfig /all
Notice under your adapter, the IP address for your Default Gateway
Enter that IP address into Internet Explorer
The user name and password should be admin
Locate the tab for your wireless setting