Follow instructions to use putty from the putty help page.
Download and install xming from this site, pictured below.
When running putty, enter "lab.cs.swarthmore.edu" in the Host Name field. Click on the "+" next to SSH in the left navigation bar, and then select X11
Select the "Enable X11 forwarding" checkbox.
Then Click open to run putty. Enter your SwatCS username and password