Vista - XP Permissions manager and security?

I posted a while ago about a problem I was having accessing XP "home
folders" from Vista in a dual boot system.

I was told that there was no way of disabling simple file sharing in XP
Home and that this was the root of my problem (no pun intended). How true
the advice was - none of the hacks and workarounds allowed me to access the
home folders from Vista (neither starting in safe mode or using takeown made
a bit of difference although takeown did allow me to at least view the
filenames but not to access the files).

Anyway, I found a shell extension called XP Home Permissions Manager (so
good that come the expiry period I will buy it). It provides Professional
like file sharing functionality for XP Home - as far as I can see identical
to XP Pro and Windows 2000.

It does the job incredibly well - except that it inserts many usernames in
the permissions list including "Everyone".

Is there a security risk in making home folders in XP available to Everyone
and other generic low level security user groups? I'm behind a software
firewall and a router so I don't think that anyone externally could gain
access. It also seems to be the only way I can access the XP Home "home
folders" from Vista. Still, I have a feeling that I'm creating a problem
here but I can't quite work out how.

Is there a way of tweaking Vista to allow Vista to access XP Home in a dual
boot system? Rather than tweaking the XP Home permissions settings?

Gareth.