Just to sort of "well actually to complicate matters further"
Apart from my original problem I then discovered that access was random whether I could access network files or not from different PC's. What worked on one PC did not necessarily work on another.
One PC would see the Vista PC but would not let me access it without a password, which it did not recognise,
(As I use the same password on on all PC's it should not have happened)
Another PC could see and access the others.
So,
eventually I managed to change the password by "having to create a second admin account" then using that account to remove my original password and then re-install a password.
(This is because Vista on a network will not let XP access a Vista PC's files without a password)
The problem then was, the original PC that was seeing all the other files was now being blocked. (wrong password)
OK, I think I should get to the point "and to the solution" the problem appears to have been caused by TWEAK UI
Yes, Tweak UI, because when using the "Autologon" feature, I guess as it is encrypting the password/s it is therefore changing them.
So with disabling/removing the "Autologon" feature from Tweak UI on all the XP PC's and replacing the password in User Accounts (albeit with the same password) on all the PC's.
Everything then worked properly.
Now, I reinstated the Autologon feature on all the XP PC's and everything still worked okay.
All this because I changed a name from "Medion to Medion1"
Not to mention it was Vista that was also the cause of the problem.
XP to XP was not a problem at all.
As long as we've all learned something at the end of the d then it was probably worth all the frustration.
I'll have to consider that statement closely.
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Dare I mention that I'm still not 100% happy with the performance, so may now go for a re-install on the main XP PC?