No, no way to do this.

This forum is powered by XOOPS -- one of the most popular systems on the Web.

You can search for members very handily. Click Members on the left side of this page.

But there doesn't seem to be a way to search for posts made by a certain member. You can sort by the poster, for example:
1. Click Main Forum
2. Click Sorted By and change to "topic poster", then click Go
3. Then find the page where the topics they started begin

This is not a search by the member, but is apparently the only workaround and is the one recommended by the Webmaster: Search by poster?

Unfortunately it doesn't show the posts they made, only the Topics they started