I would suggest downloading the Windows 7 Beta (legally) yes.. but since it IS Beta software and there will undoubtedly be some bugs in it, I wouldn't suggest getting rid of Vista completely just yet..

Win 7 is rock solid at this point in time, especially for being in the beta stage, but it's never wise to completely switch to beta software for your everyday machine..
That being said, I would definetely suggest trying out the beta once it's released by Microsoft (not much longer to wait

).. you will like what you see..

When you do get it, just create a new partition on your hard drive if you are able to and install it on the new partition.. that way you'll still be able to use Vista while trying out Windows 7 Beta 1..