Can't you just go the
repair install route? Or maybe--assuming it'll let you-- boot into 'safe mode', move the files you want to save to the big 300GB and do a clean install on the 20GB? I don't know how your comfort-level around computers, but personally, I'm partition shy; I don't like to mess around with them unless I absolutely have to mess around with them.
However, if such a road you want to take then WDM won't resize a partition without a full wipe as far as I know. I'm sitting at a work pc right now and they don't like me 'fiddling' with things, otherwise I'd check it out myself.
I don't know anything about the ultimate boot CD, so, I couldn't say whether it supports NTFS or not, but when it comes to basic partition work, I like
bootitNG. It's small, fast and free. A lot of people will point you the direction of Partition Magic and its ilk and those are great, but in this case--a simple resize--I think it's overkill.
Good luck whatever you choose
