Is 4 1GB Ram modules faster than 2 2GB Ram modules?

The simple answer is, it depends.

If the computer is set up to have dual-channel memory, and requires two sticks in a channel, then if you have two 2GB sticks, all your memory will be in the one channel. If you have, instead, four 1GB sticks spread across two channels, you will get twice the memory speed, as the two channels can be set up to read and write independently. It is like having two straws to your milkshake.

Even if you have only one channel, you can still get greater speed by having four sticks instead of two. Some memory controllers will do what is called a "four-way interleave", where they read from each stick in turn, thus getting four times as much data as they would from a single stick; it takes time for memory to get ready, and an interleaved memory access system can schedule the sticks so as to read them in a round-robin fashion, reading four times the data in the same time. However, this is uncommon except in high-end hardware.

If neither of those cases holds true, though, there is no performance advantage. And in fact, in most cases the actual performance advantage for the end user is imperceptible.

Against this, one must weigh the fact that most motherboards only have four memory slots, so if you want to upgrade past 4MB, and you have four 1MB DIMMs installed, you will have to throw them all out before you can upgrade.