After clicking the appropriate links to install the google toolbar,
"ISEARCH" is the logo on the left of the toolbar rather than "Google."
It's search results are different, and it's icons are different (at
least from the picture of the Google toolbar on the download page).

I then installed Google Toolbar Version 4, and it still has the ISEARCH
logo.

I then went to add/remove programs in control panel and clicked on the
"Google" toolbar to remove it, and when I went back to IE, this ISEARCH
toolbar is still there, and there is no more option for me to remove
the Google toolbar in add/remove programs.

Is this some sort of virus?

After uninstalling it, you should scan your computer for spyware and
adware with Lavasoft Ad-Aware, and then Spybot S&D......Scan and fix
everything....