I'm not sure what "coding WP" means, but are you talking about creating a Theme or trying to install a Theme and then edit it?
And I hope you mean "reinstall" by saying that you had to upload the original version of the theme and not totally reinstalling WordPress. Yikes.
Okay, let's see if we can help. Have you found a theme that resembles the one you want? There are tons of themes out there, just do a search on Google for WordPress 1.5 themes. When you have one that is close, upload it and activate it from WordPress admin panel.
To change the look of a theme, it begins with the CSS file, typically called "style.css" and found within the theme's folder. Do try to avoid changing the actual php files if possible.
Create a test post and view it in your web browser. From the menu choose VIEW > PAGE SOURCE. It will pop up a page with the generated HTML version of your page. Go through the code and look for the different ID and CLASS names for the different sections on the page. Then go through the
style.css file to match which style "selector" (name) matches which section.
From there, you can change the attributes (margin, padding, font, font-size, etc.) to what you want, including replacing the graphics in the header and such.
I hope this helps.