Make sure PEER SERVICES is set to process .asp files through the appropriate dll.
c:\winnt\system32\inetsrv\asp.dll

I have these files set to us the asp.dll
.asp
.cer
.cdx
.asa

I run Win2000 with IIS 5, so it may be a little different in setting up, but here is what I have to do..

Go into the
Administrative tools, Computer Management,
Choose Servies and Applications
Internet Information Services
Choose the website, right click and goto properties.
Choose the Home Directory Tab
Choose Confiuration, (near the bottom)
Now use the Add button to add new mappings...

I had to do this when I put ColdFusion on,

As I say, setup for PEER Services may be different.