Windows XP Software VPN

Hello everybody, this is my first message on this list.
I need some help with this situation:

HOME CONFIGURATION:
1 Modem-Router	192.168.2.1
2 Pc Win XP		192.168.2.4		Workgroup:  AAAA
3 Pc Win XP		192.168.2.5		Workgroup:	AAAA
4 Pc Win XP		192.168.2.7		Workgroup:	AAAA
5 Pc Win XP		192.168.2.10	Workgroup:	BBBB  (This work 24hr/day with  
Windows XP VPN client on 192.168.7.201)
6 Pc Win XP		192.168.2.11	Workgroup:	BBBB

I have two Workgroup because i share my Lan with my neighbour that use  
it's own workgroup, but it's not a problem.

OFFICE CONFIGURATION:
1 Modem-Router	192.168.7.1
2 Pc Win XP		192.168.7.2		Workgroup:  CCCC	(This work 24hr/day with  
Windows XP VPN server on 192.168.7.200)
3 Pc Win XP		192.168.7.10	Workgroup:  CCCC
4 Pc Win XP		192.168.7.12	Workgroup:  CCCC

The only ping that works now is the one from HOME 5 to OFFICE 2 both using  
MachineName or IP addresses (7.2 or 7.200) and the reverse OFFICE 2 to  
HOME 5. This two machine are directly connected via VPN Client Server.
So, i need that everyone PC in OFFICE and HOME can ping all the other PC,  
is it possible, I need to change all 2.x to 7.x ? What append in case of  
IP duplication ? Must I connect every HOME PC to the VPN server by a  
dedicated VPN Client connection or I can use HOME 5 as a gateway ?

Thanks' for help
Sorry for the bad english, Diego Settimi