You can identify DNA sequences by using some bioinformatics tools (e.g. BLAST http://blast.ncbi.nlm.nih.gov/Blast.cgi, or CENSOR - for transposon search, http://www.girinst.org/censor/index.php ), but it depends on what sequences are you searching for?
Transposons have some sequence features, introns and exons have short identification sequences.
For DNA transposon you can use RepeatMasker search which give you hits about most likely transposon family. Introns have always junction with exons (donor and acceptor sites)