If you are interested in debugging your Jscript code, then you can use Visual Web Developer (VWD) Express edition, a free download from Microsoft website. Exact instruction on how to use VWD for debugging Jscript are listed at the following blog post:

http://blogs.msdn.com/rajeshbhutani/archive/2007/04/10/debugging-jscript-code-in-ie-using-vwd-express.aspx

If you want to see these steps in action then you can watch the following screencast:

http://channel9.msdn.com/ShowPost.aspx?PostID=301814