All variants of the NXP LPC21xx series of ARM microcontroller share the same baseline features as they are all based on the ARM7TDMI-S core, the major differences between these variants is an increase in Flash, RAM, GPIO and the addition of various peripheral hardware modules such as CAN, USB, ADC, Ethernet, etc.
For example, the only difference between the LPC2129 and LPC2124 is presence or lack of the peripheral hardware CAN modules.
Another example, the LPC2114 and LPC2124 differ only in the available amount of Flash.
Therefore, code written for one variant of LPC21xx series should run on another variant of the series as long as the required resources utilized by the code are available on the other variant.
In other words, code utilizing a peripheral hardware CAN module of an LPC2129 with not function on a LPC2124, however code utilizing the peripheral hardware ADC module of the LPC2129 will function as expected on the LPC2124 as both variants have the same ADC module.
Further more, much of the code written explicitly for the LPC2148 will run on another variant of the LPC21xx series with little, if any, modifications, provide the other variant provides the required resources.
Methods of configuring and utilizing most of the baseline features such as GPIO, Timers, UART, ADC, PLL, etc, is typically universal across all members of the LPC21xx series.
I have not used Proteus in quite a while, so my advice in that area is limited.
However, a quick look at the available LPC21xx series in Proteus indicated thirteen possible options, including the LPC2124.
BigDog