There really isnt much of a difference between 32 and 64 bit. If you run a lot of new high power applications 64bit is the way to go. Your system seems to be up to par, the only thing is that 32 bit supports a bit more than 3 gigabytes of ram while a 64 bit system can support as much as you want. Personally i would go with the x86 64bit.
For only 3GB of ram you only need the 32 bit version. The 64 bit version is less efficient and has problems with drivers here and there. You'll have better luck compatibility-wise with the 32 bit version.
For the most part though, the average user would never know the difference. Windows 32-bit apps will run on either version almost the same. We run 64bit on some of our CAD workstations and have problems getting drivers sometimes. Also we have some older 16-bit apps that won't run on the 64-bit OS. The average user is unlikely to have these problems but unless you are going beyond 4GB of ram there is no benefit to the 64bit OS.
32-bit Windows will work fine with 3GB of memory. But if you ever envisage upgrading to 4GB or more then you'll need 64-bit Windows to take advantage of it, so you might consider starting off with that now so as to save the hassle of a re-install later on.
My PC runs on W7 64bit. Well your settings are good for a laptop. I recommend that you use windows 7 64bit, it will be able to handle it and plus your processor is 64 bits. Anyway you will be not able to run every game on the max setting but they will work