You have a choice of going straight to Joomla 3.0 or going to 2.5 first. Both SP Upgrade and jUpgrade have versions ready for both versions. Please consult with their documentation on how to migrate from Joomla 1.5 to 3.0/2.5.
That is well beyond my scope of expertise or the template related support we can provide.
That's why there are migrations scripts out there, they are supposed to be less than 'create a new J3 site, then cut & paste all your content' solutions.
I suggest doing some experimentation in a sub directory, sub domain, or a localhost (which I plan to do myself in the coming weeks as I have 4 sites to convert).