To install the NVidia, I would try the elrepo driver, it has worked well for me and many others.
As for wireless, CentOS 5.5, though stable for servers, may be behind in wireless support. Depending upon your reasons for choosing 5.5, (which should now be updated to 5.7), you might want to try again with CentOS 6.
Not sure what the Fedora and Ubuntu issues are, you would be better off asking on their forums.
I'm not familar with the xboot program, but unetbootin works pretty well. http://unetbootin.sourceforge.net/
You do have to watch what drive is being picked though--I think CentOS 6 fixed that, and I was sure that Fedora had, but at any rate, with Ubuntu, when using unetbootin, after installation, it booted without problems.