the XslCompiledTransform.Transform function uses alot more memory running on a x64 system vs running on x86. the more xpath is used in the xslt, the more significant the memory usage becomes, for the attached xml and xslt, its 30 mb mem used with x86, but ~400mb on x64. i attached the cs file as well as sample xml and xslt files.
use the sample like "ConsoleApplication1.exe C:\test\transform.xslt" and have all files in c:\test"
if you watch the task manager performance tab youll see the mem usage, the more spatch * = xpath) you use, the worse it gets