You need to pick up a copy of PPX first before installing Sracer's Tilson Lake xui file. The .xui is basically the compressed form of a PPX theme for easy transport.
I've setup some FAQs with step by step walkthroughs and images on a variety of subjects in PPX at the main PPX site. You can also only purchase PPX there.
http://www.ppx3k.com :)