I'd just use unrevoked as per the Rooting for Dummies guide (matlock). That's the one you want.
Though, if you do upgrade, you'll probably get a radio upgrade. You can upgrade radios rooted, but it carries a slight risk of bricking your phone (say battery dies during the process.) It's nothing to really worry about, just read up on it first.
I'd read the whole first few pages of the rooting for dummies guide. Great info there. If you do upgrade, check out the GB version of guide by ocnbreez. Top quality there too.