Installing Linux on a PC w/XP

I'm looking for different ways to load linux onto my PC. Ideally I
would like to not partition my hardrive, but am very new to the linux
world and don't know what my options are. Is it possible to run Linux
from within XP or possible buy and external hardrive and load linux on
that, so that i don't have to reconfigure my pc. Any help is
appreciated.
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