I know, the first question is "Why would you run UU on machine that doesn't have WoW installed" and the answer is because I support a bunch of guildies and had forgotten I had rebuild my work machine and had not yet re-installed WoW!
Anyway, problem is that when UU searches for the WoW.exe and can't find it it generates a browse dialog box so you can manually point to it. Even though there is a Cancel button on it, it just re-spawns the 'Find WoW.exe" dialog... forever... and ever... until you kill the process.