I'm skeptical that project can do what you ask; I'm not positive, but I'm skeptical. Let me offer a few options.
First, you could use several of the custom fields to represent minimum, maximum and most likely estimates. (e.g. num1, num2, num3). If I were in your shoes, I'd probably allocate three more fields to indicate the probability, impact and aggregate risk rating for the task, and use the combination of those to develop a dynamic adjustment to schedule. I've worked with math & formulas in project, and I'd strongly suggest that you either purchase the add-ins suggested by @david Espina, or else export to excel for the monte carlo simulation. My preference here is reinforced by your statement that you want to see a graphical representation of the confidence bars; I doubt you can do that in project, but you should be able to do so in excel.
Alternatively, if your real goal is to manage the aleatory risk intrinsic to scheduling, you could adopt Critical chain scheduling, which (at a rough summary) pushes all the risk & slack to a buffer at the end of the project, and consolidates the management.
There is a third option - what you are describing as a PERT chart is not the PERT chart that I'm familiar with. If you check Wikipedia on PERT, they describe the PERT as equivalent to the network diagram referenced by @Ashok Ramachandran, but they do reference using Microsoft Visio to create node diagrams that are related to the PERT estimation techiques you reference. Of course it doesn't lead to the error display bars you're looking for.
I think if you want what you've asked for, you're going to have to cobble it together from multiple products. In my personal opinion, the resulting schedule will be quite difficult to maintain. If you do develop such a product and document the procedures you use to maintain the schedule, I think it would be worth publishing. I can envision value in that kind of a scheduling tool and associated procedures.