Hi Paul,
I applied for the skilled independent visa on my own. It's not hard but a lot of work getting all the documents compiled. My suggestion is that you apply online to save money on sending the documents to Australia. You will need to at least have a good scanner to scan your official documents to send to where you are told to send the information.
I am not sure if the seminar you attended gave in detail of all the steps required. The Australian Immigration website is at immi.gov.au that gives information that you need. My initial recommendations for you before you actually apply is:
1) I haven't checked the required points. But when I applied back in January 2010, the points passing was 120 points. This is the min points that is required for the Australian Immigration to process your application when they receive it. If you fall a little below 120 points, you will be put on a waiting list. Not sure how long it takes but if there are many qualified applications at 120 points, I am not sure when someone in the waiting list gets selected to be processed. If you fall below 100 points, I believe your application will be denied. Please check what the new points pass is now before actually applying. I say this because there are no refunds if you apply and later change your mind. I read that they might consider only in very special circumstances. But changing your mind is not one of them.
2) You will need to have your skills assessed at the specific organization in Australia that will determine if your skills and education would be approved under that list. There is a fee to have your skills and education to be assessed. After they review your information, you should receive a letter stating your skills are recognized in Australia. Then there should be some reference number on this letter that you will need to document in your skilled independent visa application.
If you are reviewing information and have a question, there is a phone number or email address that you can find in immi.gov.au that you can contact. I had to do this on occasion when I didn't quite understand.
You can use the money that you would pay for someone else to help process your application to pay for your medical checkup requirements, police clearance,etc. This is in addition to the skilled independent visa application that you were quoted at the seminar.
I believe as long as you can understand the information and have internet access, anyone can apply for the application on their own. But you always have the option to hire someone or a company to help you. The website I documented above has a section area where you can find a registered person to help assist you. It clearly states that you need to make sure the person you hire is registered.
Good luck.