upgrading-migratingJoomla 1.0/1.5 Migration to Joomla 2.5/3.0: 

Note on Joomla Migration:
Moving from 1.5 to a newer version is a major migration. Joomla 2.5 and newer interacts with the template and any installed components/modules in a different and much better way than previous versions. Additionally, you will run into components that are no longer in use, or that have radically changed.
Note to migration, to migrate from Joomla 1.0-1.5 it is not a simple upgrade within a version but a completely new version migration. All templates and extensions have to be compliant to J2.5-J3.0. A complete review is recommend for verification on compliant solutions. It also has be installed on a new Joomla J2.5-J3.0 installation.

Note: Do not recommend maintaining the site in Joomla 1.5, it is no longer supported and has a growing security risk. Recommend before you proceed any further, you should migrate to Joomla J2.5-J3.0 and complaint extensions and template. This is a security and compliance recommendation. Please review the forum and internet on this recommendation and the risks for J1.5.

Joomla 1.5 and many of the extensions are no longer supported for that version.
I have done several migrations of J1.5 to J2.5-J3.0. I highly recommend you migrate, Joomla 1.5 is not as safe as J2.5-J3.0, you stand the risk of your hosting shutting you down and forcing you to buy dedicated IP if your site becomes blacklisted. Please review this with your hosting company and their policies.
There are some good free and commercial security extensions that can help with prevention of future attacks.
Send me a link and list of your current template and extensions, I can determine if they are still supported to migrate to J2.5-J3.0.

•    Do you have a list of your Extensions, and access to any commercial extensions, and/or template that you use?
•    Is this a live site?
•    Can you please send a link to current site for quick review?

Do you have a list of your Extensions, and access to any commercial extensions, and/or template?
I ask because migrating to J2.5-J3.0 requires all new complaint extensions and template.

The new Joomla J2.5-J3.0, has many upgrades, and since it is not a one to one upgrade some reconfiguration will be required. An example is there is no long a Section, it is just Category and Articles. The old Section will be discarded for Category(s) only!