<font color="blue">Why doesn't Apple have an AppleTV with a 300 to 500 gig drive?</font>
it uses a 2.5" drive. the largest available is 250GB, and those currently run
$169.99 at newegg. compare to
$109.99 for a 500GB 3.5".
<font color="blue">Guess my question is what is the approximate cost of adding wireless to a desktop?</font>
it looks like
you can't use an external usb drive with the apple tv, although there is
apparently a technical hack available. you can still
stream directly from an itunes pc. since you don't have wireless, one straightforward avenue for expansion might be an
airport extreme if the drive sharing feature is actually compatible with the apple tv. if not, or if you're not interested in that feature, i'd probably look for cheaper options. you won't need to add wireless to any existing systems, though, as any wireless router will cable into your network.