There is nothing against that. Just make sure that when the installer asks you if you want to associate WinBoard with PGN and FEN extensions, you untick both check boxes before you proceed. And when the installer suggests a menu group, it will probably suggest to use the old menu group of 4.2.7, which you also don't want. (Apparently it looks for the most recent menu group of similar name first, under the assumption that you are making an upgrade, and want to keep your old menu working for the new install.) Just type another name for the menu group, and you will have both groups available next to each other.
Note that to try the really fancy stuff, you should replace the winboard.exe in the install by the one at
http://hgm.nubati.net/winboard0526.zip, which contains the most-recent development version. (The soon-to-be released 4.5.0, which has the PV walk, variaton support and all the ICS enhancements, such as Seek Graph and Twin Board. For its new features, see
http://hgm.nubati.net/news.html )