Rookie Needs Help - VPN clients can't see DNS mapped drives...

I have 5 remote locations that have a Cyberguard/Snapgear VPN configured with
IPSec tunnels to my main site (main site has server, remote sites only have
VPNs).
I've been able to add all the computers to the Domain by setting the remote
PCs DNS IP address to the server's IP address. This has been working, BUT
recently the more machines I've added it seems to mess things up. Example...
I just added PC3 to one of the locations and PC2 (which had already been on
the domain) started having problems. If I login to the machine now, it takes
a while to login (DNS issue I'm assuming) and then the drives don't map
unless I use the IP address and manually map them.
I've worked on servers that have been configured before I got there. Well
this was too but now I may have to make changes to fix this issue. Since each
remote site has it's own subnet (ie. site1 - 192.168.1.XXX site2 -
192.168.2.XXX etc...) I created a new Reverse lookup Zone in DNS for each
site. I'm not sure if this was a good thing or not. Nothing seems to have
changed really but now I can see all the stations in the Forward Lookup Zone
of my Domain.
Any help is great... I'm in such a bind I'll check every little item you ask
me to if someone can help me.

Thanks,
Ron

 

A few more specs on the VPN configs:
(Example site1)
The LAN port is set to:
IP address - 192.168.5.1
Netmask 255.255.255.0
DNS Servers are the IPs given by the ISP (Should these also be the IP of my
server?)

Internet port is set to:
IP of 10.1.5.2
Netmask 255.255.255.0
Gateway: 10.1.5.1
DNS Servers are the IPs given by the ISP (Should these also be the IP of my
server?)
These have been set this way for a long time though... as I said PC2 started
having problems after PC3 was added.

I hope this helps.