An unusual tyre question

Gidday everyone I know you all get peed off with the usual what tyre should i run on my 4by or what pressure or is cooper better than micky thompsons or BFG's or will this tyre fit my wheel barrow with standard suspension or should i put 2 of one size on front and 2 smaller ones on back, anyway you know what i mean right???.......well heres a new one for ya all to think about.......you know how people use nitrogen in their tyres to run cooler?? well i was wondering if i was to fill my tyres with helium would it make my vehicle lighter? therefore creating less drag and cause my vehicle to use less fuel??? and if so , what tyre pressure should i run and what size tyre??...i suppose the more helium i use the lighter my vehicle would be??? also you think i would need a lift kit?? and what size?? oh and btw i own a Lada Niva with fuel injected VN V6 with turbo and chrome plated grease nipples Thanks everyone , hope to recieve your replies soon .......THE FATMAN