Win7 + Vista on same network problem(s)

Hi Guys,
I have following configuration:
A laptop with Vista Home Premium, and a Desktop with Windows7 Pro, both connected together via cabled network.
Both systems recognize each other on the Lan, and with the Vista box I can share files with the WIN7 box (through Password Access) BUT with the WIN7 box I can't access the files on the vista!
My Access name and/or password is rejected !!!
Those PSW are the same on both systems, I use the same home network name on both, and on both I have administrator rights.
I read a lot of possible solutions on this forum but none worked for me, so before doing any strange decision I ask you what can I possibly have overseen.
Oh yes, I also disabled the firewall on both systems but still with no access to the Vista.
Hopefully you have a solution for me. Notice I'm not a network expert, so please be clear in the description of the steps I have to do to solute this. Thankx.

I mean by this that for accessing a shared folder or drive, Win7 and Vista ask for Login + Psw, as both OS use PSW protection for drives, folders and files.

But looking further for a solution, I encounter this link:
How to make Windows 7 work with older Windows versions for networking and file sharing.

and believe it or not but removing the PSW request on the Vista box made everything work.

So now I still have a question: what's the purpose to allow PSW protection for drives, folders and files if one OS can not access to the other?