there are plugins availables which let you insert any code ( php , asp , js etc) in all pages of ur blog … i dont remember its name … you may better search or ask some body else.. it is also used for inserting adsense code in blog
i have a site
with two categories
1. news
2. articles
i want to use wordpresss for both of these cat and i want my users to be able to register once and able to post on these both diff cat ( customized form of blogs)