Hi,
Issue1 : VPN clients not able to ping/access internal PCs or resources.
Sol: 1) Check that you are not using overlapping IP addresses for VPN pool. VPN pool range should be totally different than any network which is used in your network.
2) Behind the PIX, if there is any L3 device then make sure that it has the route to reach back the VPN clients. ie. to the VPN pool assigned to remote clients.
Issue2: Not more than 1 user can connect
Sol: I belive that your contractor`s officials are behind a NAT/PAT boundary. You enable "ISAKMP NAT-T" on pix and then check out the behaviour. Here is how you can enable it :
pix(config)#isakmp nat-traversal
HTH
regards
aashish C