hi guys,
does anyone know how , and where to install software on N900, that it wont let the mobile reboot and then freeze again as happened the first time.
thanks

Did you install any thing from extras-testing last time?

Make sure the metal contacts on your battery in each slot are hugging the power terminals inside the N900 when you put it in. If they are spread apart too much in any of the slots and you give the N900 a sudden tap or jolt it could disconnect the battery from the terminals causing a reboot.
It is a quality control issue at the battery manufacturing plant.
I have that problem with my oversized battery on my N95 8GB that I bought from ebay.
If i tap the back of the N95 8GB or the side it disconnects the battery once the battery has aged about 2 months because those contacts start to spread apart over time when you take the battery out and put it back in.
I have to get a little safety pin or thumb tack to press the terminals back together tightly so they will hug the power terminals in the N95 when i put it back in.

Also don't stick files or folders on your N900 that have the same name as the folders that are already on there, i.e., don't put or create folders like documents, bin, dev, usr, etc unless you know what you are doing.

Why confuse the device?

And don't install any apps from extras testing or extras devel unless you are willing to take the chance that they could mess up your N900 but plain old extras is ok.

Never take the red pill.
Do not add any new repositories, enabling extras is ok.
Do not install everything you come across, otherwise your rootfs will be filled in no time. Make sure apps are optified when installing