OMG! Light Bulb! I know what you can do. (Too bad you didn't mention that it was on the same hosting account earlier.)
You still have the database, so you still have the posts.
Since you don't currently have any content in your new blog, this makes importing content very easy.
Basically, you'll do an 'upgrade'. Simply upload new WP 2.5.1 files to your server. (You'll need to overwrite the root files, as well as the wp-includes and wp-admin directories.) Then change your wordpress config file (wp-config) and use the database settings for your old database. This will automatically use the old posts. However, since your database was from a previous version, you'll need to do an upgrade. (WP will automatically walk you through it when attempting to view your site.)
Once done, change all of your settings such as Title, etc... Also, if you do have content from your new blog that you want to keep, simply do an 'Export' before upgrading. Also, be sure to preserve the wp-content folder.
Additionally, if you are changing the domain, you will have to follow these steps: http://codex.wordpress.org/Changing_The_Site_URL
Let me know if you have any questions.