It may be possible, but it may not be worth the money to be able to do it. As you know, natively, it not possible. However, if you change motherboards, then your Dell installation cds will nolonger work. I believe, somehow, the cds verification check is tied in with the motherboard. So changing that renders your machine a non-Dell machine. I don't recommend flashing your BIOS with a home-brew BIOS. If it does not work, it will render your machine totally useless. And it will no longer be a warrantied item.
So, in my eyes, you have two options. Forget about OCing. I am going to be frank with you here. OCing is overrated. It basically started as enthusiasts fooling around with their machines. Now, its all about buying low powered processors in an attempt to save money. You second option is to become a system builder and build your own machine. It is fairly simple, but normally your have very few troubleshooting options other than your commonsense and googling for some answers.
I typically try to persuade new system builders to head back to the game console for gaming action. In most cases it cheaper and the frustration and heartache that comes with trying to make the machine run flawless can be overwhelming. It not if your going to have conflicts is about how many. Some are easier to fix than others. In my experience, when I was a system building and doing the oc thingy, I spent more time reformation my computer with Windows than I did actually getting anything done. So, after I came back to reality, I made the transition to a dedicated gaming platform, a console. Now all I have to do is flip the switch, insert the disk, and I am in gaming heavan.
A computer is fine for regular work, web surfing, email, word, excel and a bunch of other stuff. If going a console is out of the question, then buy a prebuild system that is marketed towards gaming. I believe Dell has one, and Alienware is another company that produces gaming computers. In this fashion, you don't have to worry if you have conflicts. Call tech support and they will be able to help you.