You are confusing a couple of different things there.
The 32-bit addressing limitation. This is what you were primarily thinking of, and limits to the total addressable memory to 4GB. Note that this also includes things like video memory as well, which is why for many people it is less than 4GB. I thought I remembered Windows XP 32-Bit implementing a paging system to access larger chunks of memory, but I don't remember right off hand. At any rate running with 4Gigs of ram no matter what will still run fine, it just won't be able to address all of it.
The 3GB and 3.3GB numbers you are thinking of probably came from the hardware limitations of the first few revisions of the MacBook abd MacBook Pro. In those cases it was a hardware limitation, and I don't think any workaround has been used yet, though again I could be wrong.
And you certainly don't need Windows to use over 4GBs