download x bytes at a time over network

[Saurabh]

Heres the reason behind wanting to get chunks at a time.
Im actually retrieving data from a list of RSS Feeds and need to
continuously check for latest posts.
But I dont want to depend on Last-Modified header or the pubDate tag
in <channel>. Because a lot of feeds just output date('now')  instead
of the actual last-updated timestamp.
But when continuously checking for latest posts, I dont want to
bombard other people's bandwidth - so I just want to get chunks of
bytes at a time and internally check for <item>...</item> with my
database against timestamp values.
Is there a better way to achieve this ?