Tony, the MIT license allows modification, thats what you do when you take some part and use ii in your project. if its more than a handful of lines you should probably copy the license header and note the parts copied, especially if copied intact. Your own license header can sit before or after the pasted in bits assuming its not wildly incompatible. If you plan to make your project available via a license sensitive body such as Debian very important you have good records of what was obtained from where.
Often, people post code here or on the wiki without defining a license and that can be an issue occasionally.
On the other hand, very, very few projects don't have code 'inspired' from other projects. Concepts and approaches to a problem are not really license-able, and common sense says snippits of code are intended to be copied. The application of the term "derivative work" is a much discussed thing.
Davo