Well, there may be a virtual machine (Ubuntu) out there that the creator has already installed VMWare tools. I know there are a couple different VM's of Ubuntu on the Vmware site, look for one that says VMWare Tools Installed.
Like dinolinux said, you will get better performance with VMWare Tools installed.
But on to the question if it will run nice. I have had three different VmWare virtual machines running using VMWare Player at the same time on my WinXPPro/2Gig ram laptop, with very little performance issues. I did install these VM's myself, and installed VMWare Tools on each one.