Generally where example code is provided for another toolchain it will normally port across to the LPCXpresso IDE fairly easily. Simply create a new project within the LPCXpresso IDE, then copy the required source files across.
A few things to watch:
Sometimes, depending upon the original project, you may need to produce your own linker script, rather than use the default linker script created automatically by the LPCXpresso IDE. Details of how to go about doing this can be found in the FAQ Using your own linker scripts.
There are sometimes slight changes required to sources due to "extensions to the C language" used by source code. Typical examples are:
Some examples may contain conditionally compiling code blocks (#ifdef .. #else .. #endif). You may need to check the actual source code, any supplied documentation, or project/make files from the original target toolchain, to confirm what symbols you need to define to get the code to build appropriately for your needs.