Dear Satbir,
Renting of Generators would not fall under the category of Renting of immovable property as it would fall either under the taxable category of Supply of Tangible Goods under Service Tax or under Deemed sales i.e. Right to use under the PVAT Act. On this transaction, whether Service Tax would be payable or VAT is payable will depend on the principal of effective control.
If your company has the effective control on the GEN Set, then, service tax would be applicable. If the client/customer has the effective control, then, VAT would be applicable under Right to use (i.e. Deemed Sales).
Regards,
YAGAY and SUN
(Management, Business and Indirect Tax Consultants)