How to search and replace

[Dan Track]

Hi

I thought I'd ask this here as you guys helped me setup mrtg :)

I've got the following pattern in a text file in linux.
Target[description1].1.3.4.6.5.3.:string at 10.11.8.10
Directory[description1]: server1

Target[description2].1.3.4.6.4.9.:string at 10.17.5.24
Directory[description2]: server2

What I would like to do is replace the ip of each with the following
value of "Directory". So for example I would like
Target[description1].1.3.4.6.5.3.:string at 10.11.8.10 to become
Target[description1].1.3.4.6.5.3.:string at server1.example.com

How can I accomplish this using either C,perl,sed or awk

Thanks
Dan