Instead of downloading 'Hijacker' and making my m/c vulnerable to viruses, can I use my already installed and trusted anti-virus software 'QuickHeal' instead ?
No, HP toolbar is not a virus :) Your anti-virus will found nothing.
Hijack This 1.99.1 This is the software that we can can use to remove this toolbar. I'm not used to download the hijackthis installer, personnaly I prefer download only the executable, and I don't remember if shortcuts are created by the installer. Maybe you can try do found it in 'Program files'.
Before use Hijackthis, check in HP sofwares if you can disable the toolbar.