Technology Tree

I want to create a technology tree that is database driven. Something like this:

Tech1 -> Tech2 -> Tech3
xxxxxxxxxx||=>Tech4 -> Tech5

All of the techs follow a specific hierarchy. So if you want to get tech3 in the above example, you need to research techs 1 and 2 first. If you want to get tech5, you need to research techs 1, 2 and 4 first.

Once the layout of the database is there, I want to be able to run queries on specific techs to see what techs are needed to open that tech up. Each of the techs have numbers associated with them also, and I would like to also be able to query a tech, and find out all of the added totals for every tech that is needed to get to that tech. For example:

Tech1 (has values 1a, 2b) -> Tech2 (has values 3a, 5b) -> Tech3 (has values 4a, 7b)

I run a query on tech3, and it shows me that the totals for that tech path are: 8a, 14b. (1a+3a+4a=8a, and 2b+5b+7b=14b).

I know this is possible, but it is very complex. I have some ideas on how to start this, but I would appreciate some feedback/samples on where to get started. If someone spends the time and gives me some really helpful samples, please include your paypal in your post.