Well, it is probably too late for you, but I thought I should share my experience with pfSense and Shrewd VPN Client.
On the pfSense side, I simply followed the exact instruction of http://doc.pfsense.org/index.php/Mobile_IPsec_on_2.0.
On Windows7 I downloaded http://www.shrew.net/download/vpn/vpn-client-2.1.7-release.exe.
Here are the configurations on the shrewd side,
General
Hostname: <the server's="" ip="" address="">Port: 500
Auto Configuration: ike config pull
Address Method: Use a virtual adapter and assigned address
MTU: Obtain automatically
Client
NAT Traversal: force-rfc
NAT Traversal Port: 4500
Keep-alive packet rate: 15/Secs
IKE Fragmentation: enable
Maximum package size: 540 Bytes
Enable Dead Peer Detection
Enable Client Login Banner
Name Resolution
No WiINS/DNS server
Authentication
Local Identity
Identification Type: Key Identifier
Key ID String: vpnusers@example.com (or whatever you filled up for Peer identifier: User Distinguished Name when you set up pfSense server Phase1)
Remote Identity
Identification Type: IP Address
Credentials
Pre Shared Key: aaabbbccc (or whatever you set up for Pre-Shared Key on the server side)
Phase 1
Exchange Type: aggressive
DH Exchange: group 2
Cipher Algorithm: aes
Cipher Key Length: 128 Bits
Hash Algorithm: sha1
Key Life Time Limit: 86400 Secs
Key Life Data limit: 0 KBytes
Phase 2
Transform Algorithm: esp-aes
Transform Key Length: 128 Bits
HMAC Algorithm: sha1
PFS Exchange: disabled
Compression Algorithm: disabled
Key Life Time limit: 3600 Secs
Key Life Data limit: 0 Kbytes
Policy
Policy Generation Level: unique
Remote Network Resource
0.0.0.0/0.0.0.0
If you can verify this also works for you, it would be nice if someone could expand the Device Setup session of http://doc.pfsense.org/index.php/Mobile_IPsec_on_2.0 to include Shrewd client.
Hope this helps.
Kang Sun</the>