You have an old computer and you want to get rid of it - what do you do? I've been offered a number of old PCs recently by their owners with the expectant question "What will you give me for it?". Unfortunately, what their owners fail to realize is that a PC that is more than 4-5 years old has practically zero resale value. This is partly due to how quickly PCs become obsolete as a result of the introduction of new technologies with higher specifications and also to the fall in the price of new PCs.
Why would anyone pay you for a 7-year old PC with a 400MHz single core processor, 64MB of RAM and a 20GB hard disc drive when they can buy a 2.8GHz Dual processor, 1024MB of RAM and a 160GB hard disc drive for just under €700 (including a 17" flat screen monitor!)?
If you have an old PC that you want to get rid of you could try one of your local schools and see if they will take it. Provided it is in full working order they may. More likely they will find it too old and difficult to maintain, particularly if it is running an older OS, like Windows 98.
Your other option is to bring it along to your local recycling unit, a list for Dublin can be found here. You'll be glad to hear that these centres do not have any charge for the disposal of computers or other waste electrical items.