First, you shouldn't set your minimum amount of ram allocated to the maximum amount allocated!
something like this would be more appropriate:
"C:\Program Files (x86)\Java\jre6\bin\javaw.exe" -Xmx512M -Xms1024M -jar "minecraft_server.jar"
Based on how much memory you have you can also increase the maximum amount of ram allowed also.
If you need help converting Gb to mb: http://egret.net/kb__mb.htm
As a final tip, if i recall correctly, after 1024mb of ram java can only allocate whole #s, aka 2,3,5,7 Gb. No 2.5Gb though.