outlook attachment problem

I have an annoying problem, when I try to send emails with large picture attachments, it goes into the outbox.
Outllook then either fails to send, or makes then sent sound, but mail does not go into sent items, although later i have discovered that it has been sent.

I have been repeatedly clicking on send/receive, and hear the sent sound again, but still it remains in outbox. Recipients have informed that they have received multiple copies.

Using MS OUtlook 2002.

Have heard that there may be a size limit for attachments, but can't find where this setting is..........