Hard to say what the problem might be, but my instincts tell me to start with the PC.
Would you do the following?
1. From your PC, go to speedtest.net and do an Internet speed test. Report back on results.
2. What operating system are you running, and what are the specs of the machine? CPU type, memory, etc.
3. How many bars of WiFi connectivity do you have usually?
4. Do you have up to date anti-virus software? Norton, Symantec, etc. If so, what are you using?
5. How far away from the wireless router is the PC? How far away from the wireless router is the iPad?
6. Do you have the latest Squeezebox Server software installed?