It not only depends on the isp that is sending the files but also on the mail admin of the server receiving the files. Typically a corporate email using MS Exchange Server is set to around 10mb as I think that is the default limit - this is to limit the storage requirements for holding everybody's mail boxes.
If you know that where you are sending can receive bigger files than you are allowed to send then you can get around your ISP's restriction by installing your own SMTP server on your local machine and sending mail out through that rather than your ISP's SMT server. A program such as Easy SMTP Server - secure and reliable way to send e-mail from your portable PC (http://www.softfolder.com/easy_smtp_server.html) would suffice, once installed change the SMTP settings in outlook from your ISP's SMTP server to your local machine name.
Be warned that most most mail servers will bin email if the recipient domain name does not match the IP range it was sent from e.g. if you try sending email as
[email protected] from an Virgin Media i.p. address using this smtp software the likelyhood is the email will be treated as junk mail as the hotmail IP owner is not the same as the Virgin Media ip owner.