I jailbroke my 3g iphone with 2.0.2 using XP (I believe I used winpwn, or quickpwn)

Here's my question - I've found conflicting reports:

If I want to move to firmware 2.1 (which I see has been jailbroken), is it possible to do so WITHOUT loosing all my MANY installer and Cydia apps? IE, without having to back them all up?

I've even edited some custom winter board themes and stuff - how much of that disappears when you upgrade?