This has been already done a long long time ago....
VuDu (and others), like said before, search first
MSN Messenger saves the logs in XML format. XML means that it is structured in a certain way. However, it doesn't say how something should look (the log) if you look at it.
But when you open the XML logs in Messenger it looks very nice and all. If you open those same XML logs in Internet Explorer they look the same. How does Internet Explorer knows how MSN Messenger shows the logs? Simply, because all the XML logs have a reference to another XML file (actually an XSL-file) which explains how it should look. This file is called
MessageLog.xsl and describes how the XML logs should be shown.
In other words: just alter that
MessageLog.xsl file to show your logs so they look like the Messenger Plus! logs.
The XSL file is in the same directory as your Messenger logs. Make a backup of it first (so you don't loose the original) and then download, unzip and copy
this file over the original one.
From now on, when you open the XML logs, either in MSN Messenger, or either in Internet Explorer, they will show as Plus! logs. If you do this in Internet Explorer then you can save them to simple textfiles also.
also see:
Can I convert MSN chat log to plus! format?
For a more advanced look of the logs in MSN Messenger see:
ChrisTorng Style MessageLog V2.1
Another alternative is found here:
MSN 6 chat log viewer (enhance the MS one)
And to view the original Messenger Plus! logs there is an excellent logviewer:
http://360software.dakotabcn.net/logviewer/
PS: all could've been found with the search function of these forums.