Going from the Windows version of MSN to the Mac version is a bit of a shock at first. The Windows version has a ton of buttons, features, ads, pop up windows, annoying noises, etc. The Mac version is simplified, ad free, and without all the obnoxious stuff that comes with the Windows version. If you are used to, (or enjoy) using nudges and the like, you will have to use an application other than MSN for Mac.
Adium took some getting used to, but after finding a skin I liked, and just giving it a chance, I now enjoy it. When I am on my PC, I can no longer stand all the crap in the Windows version of MSN, (as if that wasn't obvious so far). I ended up installing Trillian on my PC because it's got a calmer, simpler interface, similar to Adium. I don't miss the other features at all.
Don't be too quick to uninstall Adium. Give it a week, and see if it grows on you.

Good luck, whatever you decide, and congrats on the new Mac.
