vpn in a vpn

Yes you can, the problem is, that when you vpn into the 1st site, your default gateway is the vpn gateway to the 1st site, so you have no gateway to the 2nd site. Depending on your VPN setup, you may be able to create a static route within it to the other site, so the road warrior VPN user won't run into the gatway issue. I have done this succesfully with ISA Server.

This all depends on how the vpn is setup...

I'll try and explain in the easyist way possible

Site A (HQ)
Netowrk: 192.168.1.0/24
Device handling VPN to Remote Office
192.168.1.251
Router: 192.168.1.254
(The Router and Device can be the same but setup will be slightly different)
Dial-In VPN Server: 192.168.1.252

Site B (Remote Office)
Network: 192.168.2.0/24
Device Handling VPN 2 HQ
192.168.2.251
Router: 192.168.2.254

Scenario A (Router + VPN Device Seperate solution 1)
On the machines dialing in set the client to use the default gateway on remote network and setup your router in the HQ to forward all traffic for remote office to go to the remote office (This Should be done anyway)
The drawback to this is that all traffic that the remote user send to the internet will end up going via your corperate office

Scenario B (Router + VPN Device Seperate or The Same)
You can use the CMAK (Microsoft) this is a free addon for windows server platforms
You can build your own VPN Client and add routes for your other network. i.e. add a static route to 192.168.2.0/24 using the ip addy of the device handling the vpn

Scenario C (Router + VON Device the Same)
Again set the default gateway on the client connection to use the vpn but you will get speed issues.