Not in general but I saw a lot Vista laptops with 1GB RAM only. Vista with less than 2GB is swapping like mad and appears frozen very often.
Mine came with 2GB and ran barely smoothly only after upgrading to 3GB, really smoothly only after upgrading to Win 7.
I don't run anything with less than 4GB, but I have to agree a bit here. If you're running Vista on underpowered hardware, or especially if you have limited RAM, it will impact all system performance (and certainly will appear in MC).
I have an older machine at work that runs Vista, and MC certainly doesn't perform quite like it did on the same PC when it was on WinXP (though I wouldn't say it doesn't "work" in any way). But I did notice a drop in performance. And, that is a fairly powerful PC for its age, as it is a Pentium D (Netburst architecture) 3.2GHz with 4GB of RAM. On older, or slower, lower-end hardware... You'll probably see lots of general performance problems.
Windows 7 is MUCH better. Take the plunge if your stuff supports it. Just make sure to wipe the machine and install from scratch. Just say no to Windows upgrade installs.