In its current state, the iPad is rather gimped at iOS 3.x and while it's good, it could be so much better with all the features that were introduced with the iPhone 4. Multitasking, folders, etc., are all missing. And frankly, with its screen real-estate, the iPad would be great at multitasking.
If you want to try out iOS 4.2 however, you'll have to be signed up to the Developer Program at Apple and register your iPad's UDID number, which uniquely identifies your device, and allows you to install a beta firmware. Registration is required because iTunes will authenticate with Apple.
So what if you don't have a developer account? Not to worry, MacGeekBlog has launched a site, allowing you to register your iPad's UDID number with them. It may take up to 24 hours for registration to go through with Apple, but once it's completed, you'll be able to install 4.2 on your iPad. We're told however, that the process actually only takes several short hours on average.
The registration is free, but signing your UDID to MacGeekBlog's dev account requires $6, which is significantly cheaper than paying the $99 fee to enter the developer program yourself with Apple.
Instructions are on the site. Check it out