PHP ob_gzhandler, IIS 4.0, and .js/.css files

I am looking for ways to improve performance for delivering content from a couple of CDSes in a Vignette solution. (which get as large as 100kb), so I am looking into HTTP compression (which looks like it can compress our files down to 12kb). I found a few commericial vendors such as Pipeboost and XCache. What I have also found is PHP solution using "ob_gzhandler" for php.ini We are using IIS 4.0 so can't take advantage of IIS 5.0's compression (and I've heard it has problems anyways). I was wondering if anynone has experience in this area, using ob_gzhandler. The only problem I see pointed out on the web about the ob_gzhandler / php is that it doesn't work well with .js or .css files (which is alright with me not to compress... ). How can we specify it not to compress .js or .css (or perhaps only .html) files? Thanks. -Edward