Where can i get the upgrade and is it safe? from my wireless service provider?

yes

I am also trying to upgrade, but am haveing trouble. Perhaps you can help?

I have Desktop 4.0 installed. Then I install Handheld 4.0. If I go to Blackberry Desktop->About->Handheld Software, I see OS 4.0 there ready to be installed. But then if I run Application Loader, it doesn't find any applications to install. The App Loader window just says "No system software to install for your handheld".

Any idea what might be wrong?

Thanks!

try deleting the vendor.xml file from C:\program files\common files\research in motion\apploader (i'm 95% sure that's the correct path) and then running app loader.