Can´t search as only one port available

I´m using a VPN-address, can connect and download, but not search.

The dc++ instructions state: You need to forward three ports: 2 ports for transfers and encrypted transfers (both use TCP protocol) and one port for searches what uses the UDP protocol. You can use the same port number for transfers and searches, but you need a different one for the encrypted transfers.

The VPN-Service I´m using is forwarding one port number to my computer and I suspect, the problem is that I need two?
Supposed it is so, what can I do about it? I tried any possible port number in combination with the one that is forwarded,
but the search simply won`t work.

My data: XP, no router, not a firewall problem.

Thanks in advance

Leo