I plan on upgrading my computer soonish. Would installing RAM at a higher speed (replacing my current 533Mhz DDR2 with 667Mhz, not adding to) make much much of a difference? Would upgrading to 800Mhz make a difference in crunching times? I'm running on a 2.8Ghz Pentium D. I could upgrade to a faster model Pentium D, I know, but that's a pain and want to wait a bit before doing that.

Pentium processors are "old". The way to go now, is "Core" processors.
Presently Core 2, with either Duo or Quad.

They use less power, (and so run cooler), and they have a larger inbuilt cache, which speeds things up for some projects.
You'll probably find that they are also cheaper than a Pentium chip, as these get harder to find.

As for faster ram, for some projects it will make a difference, for others, possibly not. But whether or not it's worth it on a Pentium cpu, is another matter.

Pentium processors are "old". The way to go now, is "Core" processors.
Presently Core 2, with either Duo or Quad.

They use less power, (and so run cooler), and they have a larger inbuilt cache, which speeds things up for some projects.
You'll probably find that they are also cheaper than a Pentium chip, as these get harder to find.

As for faster ram, for some projects it will make a difference, for others, possibly not. But whether or not it's worth it on a Pentium cpu, is another matter.

I can't afford to buy a new core 2 processor, I just have enough for a RAM upgrade at the moment. I'm not upgrading just for BOINC, I just want a computer that will be usable for a few more years before I buy a new one.

Pentium processors are "old". The way to go now, is "Core" processors.
Presently Core 2, with either Duo or Quad.

They use less power, (and so run cooler), and they have a larger inbuilt cache, which speeds things up for some projects.
You'll probably find that they are also cheaper than a Pentium chip, as these get harder to find.

As for faster ram, for some projects it will make a difference, for others, possibly not. But whether or not it's worth it on a Pentium cpu, is another matter.

I can't afford to buy a new core 2 processor, I just have enough for a RAM upgrade at the moment. I'm not upgrading just for BOINC, I just want a computer that will be usable for a few more years before I buy a new one.

Upgrading RAM is a way to breathe new life into older machines. Setting the rated speed and BOINC issues aside, I believe overall it helps when increasing the amount of RAM (256 -> 512 -> 1Gb, -> 2Gb.,etc.) of not having a system use virtual memory (swap space) as much. It is quite a bit faster to utilize RAM than the HDD.

edit- I changed out the RAM on a P4 the other day, from 1Gb pc2-3200 333Mhz to 2Gb pc2-4200 533Mhz and find that the box is a bit snappier and rarely needs to use virtual memory for what I run on it. It is dependent on what memory intensive applications are being run (I'm not a gamer per se...)

I'd suggest throwing as much RAM @ as fast speed as you can afford. And not necessarily the high dollar stuff like Corsair (there is a cheaper line by the company called "Value Select"), I'd suggest PNY (never had any problems with the brand and it is priced reasonable)

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I plan on upgrading my computer soonish. Would installing RAM at a higher speed (replacing my current 533Mhz DDR2 with 667Mhz, not adding to) make much much of a difference? Would upgrading to 800Mhz make a difference in crunching times? I'm running on a 2.8Ghz Pentium D. I could upgrade to a faster model Pentium D, I know, but that's a pain and want to wait a bit before doing that.

For many BOINC projects, RAM bandwidth is a bottleneck, so having a faster one will definitely be helpful.

Just make sure your motherboard supports that speed, or you would end up wasting money...

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