The reason that I asked for the ssytem manufactuer and model...is that some versions of systems (Media Center Edition systems) which were sold by the various OEMs (Dell, HP, etc.) all came with NET 1.1 installed and the owners of these systems should not attempt to uninstall that version.
It's a fundamental part of the Windows install...on those systems only.
On the other hand...any version of NET Framework which is not on an MCE system and was not installed as part of the O/S...can be removed. Reasons for removing would include a damaged version, which may lead to unexpected errors.
At today's date, all of us who don't have an MCE system...can probably get by with removing all versions...and then installing either NET 3.5, SP1 or NET 4.0.
Another point...the only systems that really need to have NET installed...are the MCD systems and any system whereby having NET installed is a prerequisite for installing programs/drivers. ATI drivers call for NET, as does the nLite program. Those are the only two instances I have experienced, but there are others. My experience is that such programs will clearly state and otherwise indicate that some version of NET is required before proper installation can occur.
Tool for uninstalling, Dotnetfix Cleanup Tools - http://cid-27e6a35d1a492af7.skydrive.live.com/self.aspx/Blog_Tools/dotnetfx_cleanup_tool.zip NET 3.5, SP1 Download