I wouldn't go as far as to write the lesson plans out and do all the work for the teacher, with your "aid in preparing resources for ICT" i would put the emphisis on 'aid'.
I personally would go as far as to go over a draft lesson plan with a new teacher or one without many IT skills and say what is and isn't possible on the school systems and load up any additional files or software that was needed, check the IT room was working fine. Generally give advice, but would leave writing the final lesson plan to the teacher, afterall they are the ones who should know the syllabus and topics to be covered not us.
I've been asked to be present in the odd lesson before with some teachers to troubleshoot any problems that come up, but on the whole the staff where I work are ok with using the computers, and come to my office which is next to the most regularly used IT rooms when they have any unexpected problems.
If your happy to take a more active role I would try and get your job changed to more of an ICT co-ordinator position as Nij.UK says, and get your job description a bit better defined.
Daniel