I'm looking for a tool (or a set of tools) for Windows that will perform the following:
I've already got 1 and 2, but I can't find a tool to do 3.
For capturing I can use Wireshark, for playback Colasoft Packet Player, but I couldn't find a way to change the host the packets are sent to.
The tool should work on Windows XP SP2/3.
You mention Colasoft Packet Player and it sounded like a useful tool, so I checked it out. While checking their site I found they also have Packet Builder.
It seems this tool can import pcap files (and some other formats) and edit them. It can then export the edited packets again, but only to Colasoft Capsa Packet files (Colasoft's own capture file format). But that should not be a problem as Packet Player is be able to read their own format.
Unfortunately it seems there is no way to edit multiple packets at the same time, so it's a tedious process to edit a lot of packets.