i think the issue is the security aspect of CS 2.0. I remember reading a couple of years ago that one of the big reasons for CS 2.1 was to close security holes in CS 2.0. maybe I over-reacted and went to CS 2.1. perhaps Alex Chrome can comment on how critical/non-critical this is.
CS 2.1SP3 was definitely a "no go" with ASP1.1 on Win2003. We had to upgrade to ASP 2.0. The unfortunate situation there was that a combination of Windows automatic updates and test install of dotnetNuke on the same server rendered 2.1 unusable. I simply could not get 2.1 up and running again after about 3 months of running find on 2.1SP3 ASP 2.0. We ended up moving to 2007.1. That version has been very stable. It has not gone down in several months whereas 2.0 and 2.1 had major problems every time our Windows server was bounced.
All of this may be specific to our case but some things to keep in mind based on my experience.