You can install the microsoft fonts from the rpm supplied by www.mjmwired.net
(you'll have to hunt - but there is also lots of good fedora information there.)
Then you can just use the gnome fonts dialog to change to whichever one you want. The dialog is in the main menue under preferences.
If you want a good similarity, the "sans" fonts look like tahoma or arial and times-roman looks like times-new-roman.
However, if you play around you'll find fonts that actually feel better than the microsoft ones you are used to. The essence of linux is variety - customise to your own specs