I plan on buying a vostro v13 that does not have a HDD.

I want to SWITCH my current laptops HDD (from a inspiron 1545) into the vostro v13.

They are both build for 2.5 sata and both laptops are dell.

I heard that I will need to reformat the HDD and have a new operating system DISK, is that true?

And would I need a brand new operating system pack or would I just need the re-installation disk? You will need to install the OS from scratch on the new laptop.He can image the existing hDD just in case...
Then he can install the existing HDD and RUN a Repair Install...depending on the OS it should work out fine...

More details.
Also if the above FAILS he can do a Factory restore from the hidden partition...

Those are the options i see available...patio - the repair install would work only with XP to the best of my knowledge - and he'd still need an XP CD. As for a factory reinstall, the new laptop doesn't have an hd so I'm not sure what a restore from the hd of the old system to the new ONE would accomplish - it's two different systems. Unless I'm missing something???I've done the Repair install all the way up to Win7...
Does it work everytime ? ?...No.
As to the factory restore he is looking to re-use the old HDD...not a new one...so that would work as well.
Until we get more info as to what he wants i was just suggesting options to make an old HDD work in a newer - HDD laptop...that's all.