Yes, there are a couple of ways:
1. Click on a member's username to see their profile. scroll down & click on "see last posts of this member". This will bring up all their posts in reverse date order, 10 per page (I think).
2. Click on the main "search" button at the top of the page. Leave the main search box clear, and put the member's username into the box on the right.
Method 1 is probably easiest, as with 2 you need to spell the username exactly.
Hope that helps!