What are the specs on the system? Maybe more RAM will help here.
You may also try to do a search for a script that can copy and/or move files around based on size/date/whatever. vbscript is a good one to use for Windows, I've used it before to sort and move files about. This would be a good start http://www.webmasterkb.com/Uwe/Forum.aspx/vbscript/23778/vbscript-move-files-older-than-180days-based-on-modified-date
Scripting would be much faster and less prone to crashing than doing it manually with the Windows GUI.