FSX is forcing me into Vista.

[x_jasper]

MSXML4 is nothing to do with Vista, and might be partly related to Service Pack 2 in as much that SP2 might install MSXML4 as a matter of course.

Not an expert in this, but I think possibly MSXML4 might microsoft's XML parser. Basically a small file which allows WinXP to recognise XML structures, which FSX uses.

XML is microsoft's own mutation of SGML.

Jasper