See if this helps:
1.type msconfig in the Search programs and files box, and then click msconfig in the Programs list.
2.In the System Configuration window, click Advanced options on the Boot tab.
3.Click to clear the Maximum memory check box, and then click OK.
http://i1013.photobucket.com/albums/af254/Jaquith/Boot_OPT.gif
4.Restart the computer.
you will have your 4 gb memory back instead of 2gb.