Is their a user friendly linux operating system to replace windows pc?

Yes. Go to distrowatch.com and pick any of the top 10.

hi i also have interest in replacing Windows CE(windows mobile) on my smarthphone(arm arch)
i digged a few pocket os's android,GPE, OPIE. Currently my problem is... kernel compilation for arm XScale arch

choose ubuntu if your new to linux

distrowatch gives an clue as to whether a distro is still updated/maintained and if it's a desktop or server or media or a special use distro.
if you want to read real people's opinions in forums, you can search back 1 or 2 years. i like to search with words I imagine people use when discussing:
versus
vs
"user friendly"
512mb
1gb
p4
piii | pentium3
"core 2"
gf4
ddr2 (that one probably not a good search word)

so, example
userfriendly intitle:ubuntu intitle:vs 512mb inurl:forum | discussion "office apps"
was too strict a search. a little editing gives:
http://www.google.com/search?q=userf...dr=all&num=100
more editing:
http://www.google.com/search?tbs=sbd...g+forum++p4+vs
http://www.google.com/search?tbs=sbd...ii+|+athlon+vs

torrent a few distros, liveusb to try them. http://www.google.com/search?q=unetbootin+liveusb
(i ran unetbootin from windows, not usb. maybe that's also easier for you.)

My recommendation is AntiX MX.
http://antix.mepis.com/index.php?title=Main_Page
http://www.mepiscommunity.org/download-links
http://www.mepiscommunity.org/support

Why the ad for passwords I don't know on a 2010 post about PC linux.

Yet another spam entry point test...