I have a new 8800. I have ever used Nokia phones and I have some problems...
Where can I see the memory used and free?
I want to install a MSN client...what is the best software? When I use it I pay or the gprs traffic is in the 500 mb included?
Others usefuls software to install?

Steve, JiveTalk is the best instant message client out there...
it and others are listed here:

What Instant Messaging programs are available? - BlackBerryFAQ

Good luck, welcome to the Forums.

Thank you! With Nokia I send by bluetooth files to the phone...and I install... is possibile with blackberry?
I have downloaded some themes but I have problems to install....

You cannot install by Bluetooth.

You can install some files Over The Air, some via your PC.