Web Design and Implementation Practices

Dear ASP.NET users,
NOTE: Please bare with me. I'm a recent college graduate with some experience in VBScript and ASP 3.0. I've been recently hired by a local company as the junior ( and only! ) ASP.NET developer. I've never made a complicated site in ASP.NET, only simple little examples of functionality.
We have designers at our company who create mock websites for clients to approve before we do the work for them. Idealy, I should not have to worry about 'HTML' and 'design code' because it is my job to add functionality to the design. The designers at my company are using Dreamweaver to create these mock pages.
The mock pages use objects common in all of the pages, objects like 'navbars', 'headers', 'breadcrumbs' and 'footers'. In ASP 3.0, I could just use #include to access the code from seperate files. Currently in ASP.NET, I am just copying that relatively static HTML code ( header, etc ) to each page, then filling the dynamic areas ( ie. listings products for sale with ADO ) with the data controls as needed.
I understand that Master Pages would be effective here, but I'm new to this and don't want to jump in deep, yet. I've also seen ASP.NET code that uses a Custom Control for the 'left-hand-side navbar'. While I'd like to avoid custom controls, if possible, I'm not sure I can entirely. I might have to make the breadcrumbs my FIRST custom control.
I guess my questions are :
What is the EASIEST way for me to use HTML designers create and implement it in ASP.NET?
How is this done in the real world? And ... Is the process of designing in Dreamweaver, then implimenting in ASP.NET, normal for a web software company?
What is the best way for me to approach the problems above, as a beginner? Can I use #includes like ASP? Or am I looking at custom controls to do this?

Thank you for reading this and any help you can offer.
Sincerly,
AndresWelcome to the ASP.NET forums, Andres, and congratulations on your job.
ASP.NET offers a featured calledUser Controls that is similar to the idea of #includes in ASP, allowing you to reuse code across pages in a website. You will surely feel comfortable using User Controls. Note that User Controls are not the same as custom controls, the latter indeed being more complex.
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Edit: The bold word above is a link to a tutorial on User Controls.