I'd recommend Linux MInt, the KDE edition of it:
http://blog.linuxmint.com/?p=1927 In my opinion this is the most advanced and interesting of the Linux desktop environments and your machine should run it no problem. It can be very similar to Windows but adds some very nice functionality Windows lacks. Also check out LibreOffice which comes with it for free and is a very nice MS Office alternative that is file compatible with MS Office files. Firefox or Chrome are good browser choices, I prefer Firefox myself. The included (with KDE) Dolphin File manager is also very nice. Overall, KDE strikes me as the most polished of the desktops and it has been around for a long time.
I liked Gnome as an alternative until Gnome 3 simplified it to a fault. Still, I personally like KDE better and would encourage you to try it. There are other excellent desktop options as well that run great on lesser PCs but since you can run KDE, why not just do that is my view.
Mint is nice because it doesn't make a big deal about including and installing proprietary drivers and codecs, making the installation of a fully working desktop a breeze. Ubuntu seems pretty good this way too but by default you'd be stuck with Unity which is an ugly, simplified, inflexible take on the Mac UI. That of course is just my opinion too but Unity is early in its development and it shows.
I just went through this same exercise with a laptop myself and tried the following desktops on it: LXDE, Xfce, Unity, Gnome 3, KDE 4.x (I forget the revision but it was the most current stable one). I tried them all using Linux Mint except for Unity which I tried with Ubuntu of course.
Ubuntu and the Linux Mint flavors are available as "Live CDs" so you can boot those from the DVD drive without installing them to test for compatibility, driver support, etc. and see what they are like. So you might like to download and burn a number of ISOs, burn them to discs and check out a few flavors to decide for yourself which you like the best. If you haven't had any reason to burn ISOs any time recently, the Linux Mint install pages tell you how to do that.
Once you've installed whatever you choose, check the package manager for games. You'll find lots of stuff to fool with. If you like strategy games, you might like to check out the free Warzone 2100 or Wesnoth games. You can also get a native Linux version of DOSBox to run DOSBox GOGs with. I setup one (Heroes of Might and Magic) to run in Linux and it worked flawlessly. Also in the package manager grab the latest version of Wine and you can run a fair number of Windows games with that as well. Google for "Wine appdb" for a database of what works well and doesn't, workarounds, etc.
I hope those suggestions are helpful. Enjoy checking out Linux. I think it is a great system for a laptop like that. I've even been tempted to add a partition to the hard disc on my main PC to run it, I liked the KDE desktop and apps so well. I may do that yet.
Oh, one last thing. In my experience of installing Linux on a laptop machine I found I needed to be connected to the net via ethernet so I could download a proprietary Broadcom wireless driver before the machine could connect on its own wirelessly. So to save some time and headaches I'd recommend being prepared to plug in with ethernet when you run whatever installation you wind up deciding upon. That way the Internet setup part of things will also run just fine for you. Once you've got your driver you can of course unplug and be all set with wireless from then on in.
