HELP PLEASE

ok…so I am using wordpress 2.3.3 because that was the version that was automatically installed when I used godaddy to do the wordpress install. Now everything was working fine but I wanted to do a redesign on the site so I was looking at new themes. My theme knowledge is very limited but it has never been hard. So I found a theme that I LOVE and I purchased it and downloaded the zip file. Now when I uploaded it to my server the theme shows up in wordpress but when I choose it it looks blank. If I go into the file everything seems to be there so I am not sure what is missing.
No I called the technical help for the website that I bought it from and they said that I have to use wordpress 2.0 and I guess I figured that wordpress themes would be backwards compatible. I do not want to downgrade… I wish I could figure out how to upgrade.
Since everything is there and I have all the files I feel that there must be a way to fix it if I get my hands in the code…but I dont kno where to start.