so in your mind would you recommend that i switch from ubuntu to mandriva
in my mind - yes, but i am biased towards mandriva, its what
i am comfortable with - and my pc is comfortable with it
there are hundreds more versions of linux, a lot with live cd's and most are free,
all it takes is the time to download and the cost of a blank cd
here is a list
http://www.livecdlist.com/and this is distrowatch, it probably lists all the linux versions there are
http://distrowatch.com/don't give up, there will be one you fall for and the rewards for learning (and playing with compiz

) are limitless,
just reading your first post again,
when you boot a live cd its loaded into your physical memory, you do not need a hdd, everything will seem slow,
you can check that (nearly) everything works and whether you like the GUI (general user interface),
anything you download will not be saved, anything you change in the live version when you are running it will not be saved,
e.g - uninstall firefox and install opera -
once you exit the live cd, it will revert back to the state when you first burnt it (as its read only) and the pc will never know linux has been running,
there is also an option to install to a usb memory stick/flash memory - or maybe an sd card (i have a homemade bootable linux flash drive and a spare sd card

)
options, options
as for your regular pc - thats another thread, i think