jabber.el has limited support for file transfer. The most important limit is that files sent and received are kept in buffers, so Emacs must be able to allocate enough memory for the entire file, and the file size must be smaller than the maximum buffer size.1
jabber.el is able to exchange files with most Jabber clients (and also some MSN transports), but notably not with the official Google Talk client. The Google Talk client uses a different file transfer protocol that, at the time of this release, has not been published.
[1] The maximum
buffer size is kept in the variable most-positive-fixnum. On
most 32-bit systems, this is 128 or 256 megabytes, depending on your
Emacs version.