There is no such thing as Windows Messenger 6.0 or 6.1...
It is either Windows Messenger or MSN Messenger. Both are two different programs.
Also "6.0" or "6.1" doesn't say a thing as there are different builds for each MSN Messenger version. So do you mean 6.0.0602, 6.0.0601? 6.1.0211, 6.1.0207, 6.1.0203, 6.1.0202, 6.1.0155, etc...?
Also, older version have some major security bugs and some are even blocked so you can't use them anymore unless you upgrade.
Read:
Difference between Windows Messenger and MSN Messenger
Difference between Windows Messenger versions
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