Hi,
Is the above setup working with firwall disabled?
The logs shows the inbound UDP drops. But the TCP sent and receive works fine. We can try TCP ecapsulation of IPSec and ISAKMP packets. If it's not mandatory for you to use UDP then make sure you enable it on both ends (client and headend device).
Router: crypto isakmp ctcp port
ASA: crypto isakmp ipsec-over-tcp
Found this link, may be of your help in changing the policies of Windows firewall,
http://windows.microsoft.com/en-us/windows-vista/open-a-port-in-windows-firewall
TnR,
RV