Even on with the first installs here of 7 for the first 32bit and first for the 64bit some interesting problems came up but were seen to. The 64bit was installed on a separate before the second being a dual boot with Vista on the first. The separate install failed right off for some unknown reason.
The second being a custom install to the second primary not upgrade over Vista by any long shot proved strong while the first custom for the 32bit 7000 foobar city! I later setup a stand alone dual boot of the existing XP install with 7 on the second drive with the Vista host unplugged isolating the Vista boot sector from change. So far so good despite a few software bugs at times.
The old boot off of the dvd for a clean install or second partition option not replacement generally will avoid problems unless you are ready to try and try and try even again if something else gets in the way preventing a good upgrade just because there are all best described as builds for "testing and evaluation" not consumer ready products.
Beta is risk for the novice user while the advanced plans on disaster recovery if one of the builds go "cccccrashhhhh" for some reason. MS recommends a separate machine even while many will have a separate drive or planned a second primary for 7.
If you already have the 7000 on dvd go ahead and nuke the primary for a clean install. If the 7068 you have sees another problem you simply reinstall the 7000 fresh again or a better source for the 7068 remembering it's only "temporary" installations being seen until the real Windows 7 finds it's way to the retail shelves.