remote install on ftp using free wp domain, & does install.php need markup?

greetings,

i have successfully installed wp on my local WAMP testing server, no problems. i am trying to install on my hosting – biz.nf -but i don’t currently own any domains. so i have the free wp domain – mysite.wordpress.com – but can’t seem to integrate the two.
two things:

• i try to add my mysite.wordpress.com to “host a domain” in domain manager of cpanel for hosting, and get error “This domain name already exists in our system.” i realize i may need to ask their support, i just wanted to mention it. (i can’t think why it would say that as i just started using them. havent done anything with domains. maybe it recognizes the wordpress.com part and thus is saying i can’t do that. so, should i be able to do that, or must i my own domain?
• this may be a moot point depending on answer to previous item. i have successfully uploaded the unzipped worpress install folder to this hosting’s ftp. i navigate in chrome to the remote wp-admin/install.php file, and it displays the source code including the php code. it doesn’t execute and start the install page.

  it’s been a while and i am out of practice with php, servers, all this stuff. so is this because i dont have a domain hosted, and / or is there markup i need to add / edit to start the remote install?

if it helps, i have already configured the remote MyPHPadmin’s db, user, pw, so it’s ready to go.
thanks!