Just disable UAC, I've never had problems installing/playing games with Steam installed to C > Program Files\Steam.
That being said, I dropped a 2TB WD Black in my rig 6-8 months ago and had steam installed directly to that (previously on the SSD, 2-3 games at a time) -- there was definitely a little delay when launching the steam app. When I just swapped my SATA2 SSD for a SATA3 one, I went with the beta client installed on the SSD, Steam Apps folder in G > Steam\SteamApps. Just copied it from the previous install, had to click "install" on each game the first time, but it detects the files and just does what it does without downloading them again. Now Steam launches faster since it's on a SSD, and the games are off wherever. Plus if I know I'm playing X game every day, I can install to C (SSD) and leave everything else on the WD Black.
TLDR: Use the Steam beta client. Install games to wherever you want.