This guide will help you install tcl/tk 8.5 from source. Most distributions ship version 8.4, so in order to enable anti-aliasing or just to make your tcl/tk applications (aMSN included) look better, you'll have to upgrade on your own.
If you like, before you try this method, you may consult your package management system to see if you can get a copy of 8.5 from there. Otherwise, read on!
Go to this SourceForge page and download the latest offerings under 8.5 (at the time of writing, tcl8.5.1-src.tar.gz and tk8.5.1-src.tar.gz), you need both the tcl and tk source tarballs.
cd <download directory> tar -xzf tcl8.5.1-src.tar.gz tar -xzf tk8.5.1-src.tar.gz
Note to 64 bit users: add --enable-64bit to the both configure lines.
cd tcl8.5.1/unix ./configure --prefix=/usr/local --includedir=/usr/local/include/tcl8.5 --enable-shared --enable-threads make make install
cd ../../tk8.5.1/unix ./configure --prefix=/usr/local --includedir=/usr/local/include/tcl8.5 --with-tcl=/usr/local/lib --enable-shared --enable-threads --enable-xft make make install
Remember to be root, or sudo, for the make installs.
Use 8.5 as default
Don't skip this step, if you do, you'll have 8.5 on your system, but you'll still be using 8.4.
cd /usr/local/bin ln -s wish8.5 wish ln -s tclsh8.5 tclsh
There you go. You can remove tcl/tk 8.4 if you really want to. You will want to reinstall aMSN to make use of the upgrade.