If the pix is already up and running . Just need to add the VPN config
nat (inside) 0 access-list no_nat
sysopt connection permit-ipsec
ip local pool VPNPool 192.168.253.1-192.168.253.254
access-list no_nat permit ip [INTERNAL_IP_Scheme] [VPNPOOL_IP_Scheme]
access-list l2lvpn permit ip [INTERNAL_IP_Scheme] [VPNPOOL_IP_Scheme]
crypto ipsec transform-set 3DES esp-3des esp-sha-hmac
crypto dynamic-map [DYNAMIC_MAPNAME] 10 set transform-set 3DES
crypto map [MAPNAME] 40 ipsec-isakmp dynamic [DYNAMIC_MAPNAME]
crypto map [MAPNAME] client authentication LOCAL
crypto map [MAPNAME] interface outside
isakmp policy 10 authentication pre-share
isakmp policy 10 encryption 3des
isakmp policy 10 hash sha
isakmp policy 10 group 2
isakmp policy 10 lifetime 86400
isakmp nat-traversal 20
isakmp identity address
isakmp enable outside
vpngroup [VPN_GROUP_NAME] address-pool VPNPool
vpngroup [VPN_GROUP_NAME] dns-server [INTERNAL_DNS_IP]
vpngroup [VPN_GROUP_NAME] wins-server [INTERNAL_WINS_IP]
vpngroup [VPN_GROUP_NAME] default-domain [DOMAIN_NAME.COM]
vpngroup [VPN_GROUP_NAME] idle-time 1800
vpngroup [VPN_GROUP_NAME] password [GROUP_PASSWORD]
username [USERNAME] password [PASSWORD] privilege 1
NAMEs is brackets can be replaced with whatever you want. IP Schemes should be replaced with "10.2.2.0 255.255.255.0" (substitute your info where appropriate.)
Here is the cisco page on client VPNs
Hope this helps.
Brent
Systems Engineer / Consultant
CCNP, CCSP