Make sure you use encryption (128 bit WEP is fine).

Don't broadcast your network name.

Scan for any neighbouring networks. To minimise interference, use a channel which is at least 5 channels away from any that your neighbours are using. If that isn't possible then talk to your neighbours and devise a scheme that will work for all of you.

Twin-aerial routers have good coverage to front and back and less out to the sides so angle your router to optimise the signal for both the squeezebox and the PC.

Some people had performance issues with SlimServer 6.2 but the 6.2.1 beta is much better so download that instead.