I think all you have to do is port forward 3389 on Router 1 (WRT150N) WAN IP <--> LAN IP ... meaning public ip address to 192.168.1.1 (router default gateway).
Then on Router 2 the WAN IP address should be Router 1's address of 192.168.1.1. Router 2 should port forward 3389 from WAN (192.168.1.1) to Home Server address 192.168.2.x ... not Router 2 LAN ip 192.168.2.1.
This make sense? Not sure why you'd need to mess with subnet mask. If your router 2 is talking with router 1 and vice versa, you're set.
You're just trying to get Remote Desktop Connection traffic across port 3389 to forward all the way to your server.
I'm confusing myself trying my best to explain this clearly.
Thing is, I'm probably missing something here or there might be a better way to do what you're asking ... or at least more secure like SSH, but I can't seem to think of anything at the moment.