sounds like you might have been hacked.
if you can, get some help from someone you trust to do the following:
1) use FTP to make a copy of your .htaccess file from your public_html folder
2) use FTP to make a copy of your wp-content folder to your hard drive.
3) look in your wp-content\plugins folder, make a list of the plugins you have there, then go download fresh copies of them all.
4) delete the wp-content\plugins folder on your hard drive (you can’t trust any of the php files which were on your website, anymore)
5) look in wp-content\themes, make a list of the themes you have then go download fresh copies – or find a new theme you like.
6) delete the wp-content\themes folder on your hard drive, again, you can’t trust php files.
7) look for wp-content\uploads if you have one (I can’t recall if wp2.1 actually has that or not). If you do, check that there are only jpg, gif, mp3 or whatever files in there, no file types you don’t recognise! certainly not .php files in there.
8) if in step 7, there’s no uploads folder then find the folder you use to store all your uploaded pictures etc, download that to your hard drive and remove all unknown file types from there.
9) once you’ve done all this, make a copy of your wp-config.php from your public_html folder – you’ll need this to fill in the information for your new wordpress installation.
10) remove *everything* from your public_html directory on your hosting space. It’s a fire sale, everything must go!
11) download and install a fresh copy of wordpress as per the instructions on this website. Please note, you will be performing an upgrade, so you must follow the upgrade instructions. Use the settings from your old wp-config.php in your NEW wp-config.php
12) upload the .htaccess file you downloaded in step 1.
13) upload your *cleaned up* wp-content folder which you downloaded in step 2, into your public_html folder thereby overwriting the one that’s already there from the new wordpress installation.
14) login to your wordpress installation using your old username and password.
15) upload your newly downloaded theme to wp-content\themes then activate.
16) upload your newly downloaded plugins to wp-content\plugins and activate.
17) spend the next week getting things just right, again… and kick yourself for not keeping your wordpress up-to-date, and thereby allowing your website to be compromised.
…
lots of steps, but it needs to be done — if you shortcut this, you will probably end up with stray hacked files sitting there waiting to compromise your site again.