Windows XP Home? This would indicate, to me, that you are a simple user at home attempting to run a website, using a simple home computer, connected to a simple residential ISP.
Other than the various warnings I would voice concerning the EULA, TOS, AUP, etc. your ISP might hold that strictly prohibits any webserver or SMTP server (as most ISP's do, especially broadband), I would ask you one thing:
Why not use your ISP's SMTP server?
If your ISP provides you with an e-mail address and POP3 access, then you can configure PHP to use their SMTP server to send mail for you. If you look in your php.ini configuration file, you'll see two settings, like so:
[mail function]
; For Win32 only.
SMTP = mail.telstar-online.net
; For Win32 only.
sendmail_from = (link in profile)
Simply fill in the correct values (it's probably just like mine; "mail." followed by your ISP's server, though if you can't find the correct address let me know) for both settings and try a simple call to mail().
You might take note that PHP's mail() function does not authenticate with the SMTP server, nor does it support such authentication (at least in PHP 4, no clue about 5). If your ISP requires SMTP authentication, you will probably need to look for an alternative to PHP's built-in function.
Such an alternative might be the PHPMailer class.