Trade Mark question: if someone got a trade mark "iMall" already. Is it OK for me to register iMall99.com?

Here in the US there is a thing called Common Law Rights to a mark. Which means even if the mark is not registered if you can prove you used the mark first then you can oppose the use of the mark by someone else.

With that said from the links you have provided it seems that someone tried to trademark the mark and failed. You can use the mark as long as the person who originally had the mark 1. doesn't mind and/or 2. you are not using the mark on a similar good or service.

So yes you can try and register the mark as long as you are not using the mark for the same purposes as the other person is using the mark for which is:

Class 35: Advertising and Business Services

Providing a global computer information network site for business and/or individuals who desire to promote, sell and/or advertise their business, goods and/or services on a global computer information network; marketing services via a global computer network; and other electronic media services included in class 35 of a marketing, advertising or consultancy nature

Class 41: Education, Sport, Culture

Education services and providing of training in relation to computer information networks, telecommunications and electronic media; services in the nature of conducting seminars

I have no idea what those sites you are looking at are.
The trademark authority in the US is the US Patent & Trademark Agency (www.uspto.gov)

iMall is not trademarked.
"Succeed iMall" is trademarked = if you are in the same industry/category as this company I would not use iMall in any part of your name.

commerce marks (manufacturers) tell your purchasers that the products and centers on which they are used come from you. Your form is important and with a view to guard it, you may desire to sign up it as a commerce mark. hyperlink in source