This stuff isn't necessarily that complicated, but it's not always obvious how to implement this in Excel. Engineers-Excel.com has some great tips and even spreadsheet templates for scientific computing on a piece of software that you a) don't have to install from source code, making sure you have all of the dependencies (although if you're a scientist you should know how to do that!) or b) don't have to license annually for an outrageous fee (I haven't downloaded my Matlab updates because I can't go through the arcane licensing confirmation process without help from our IT guys).
Here is another page with hints for how to generate random walks in Excel, from the website of a Cornell physics professor. If you explore that site, you'll find all sorts of good stuff for scientific computing.