I have 3.5GB ram and with hard i can maintain 1.5gb free. If i play a game or do something that process a little the pc i get just 400mb free ram and that slow my pc the graphic of a game start to mess up.
Is there a way to have a good memory on x32 or i must upgrade it to x64?
CPU E8600
3.5GB RAM
That should not have any real issue on the graphics performance of your games...unless you are running a system with integrated graphics, in which case game performance will not be great at any rate.
I am guessing that you mean that you have 4gb ram on a machine running Win 7 32 bit, right? Most games are still 32bit anyways, and will run no better in Win 7 64bit than they will in Win 7 32bit, which is their "native" environment anyways.
Do not be fooled by "available memory"...Win 7, as Vista before that, does a good job freeing up memory when an active application calls for it. With the amount of ram in your system, "free memory" should NOT be an issue. You may have a bottleneck somewhere else in your system, but I doubt this is a memory issue.
There are a number of good reasons to run a 64 bit OS, but for most folks, game play performance is not one of them.
P.S. Although Tews is correct in that you can free up system resources by not running features/functions, that really should not be necassary, and as you correctly noted, only prevents you from accessing needed functions and programs. You should only disable start up options that you truly will not need or miss!