Ok, if you are running a P3 or celeron, all you need is a peltier 55W (from different people's experiences). Then all you need is to get a good air cooler. The P3125 is a powerful sucker that can do a good job of cooling the hot side of the peltier. For almost the same performance but almost half the price, go for a Vos32. I have 2 72W peltiers cooling my water reservoir right now. They are being cooled by 2 vos32. These seem to do a good job. So, I would recommend a 55W peltier from a good source. I would not get one from peltec. A lot of places don't sell high quality peltiers with dT of around 60-65C. High quality peltiers are those with dT of around 70-75C. So far, I know of only 2 places that have these high quality peltiers: swiftnets.com (not sure if Gabe sells them by themselves though) and Leufkens. If you use peltiers, don't bother with the peltiers from other vendors. They are mostly crap. I have bought 72W peltiers from various different places and so far they have been disappointments. 55W peltiers go for around $18. Then a vos32 from millisec.com is around $29. Get some closed cell foams to insulate the cold side of the peltier from the air (no condensation=no water puddle) which costs another $1 or so. For around $50 or little more, you can have a subzero degree cpu that you can overclock like heck.
This is a decent price. As long as you are clear in what you would like to do, it will not cost too much money and will give you a nicely overclocked system. However, if you have more money and don't want to expose yourself to the dangers of peltiers, then I would recommend water cooling. Water cooling is not that expensive (well not as much as the horrific prices most if not all vendors are charging anyways) to produce. You will need the following:
1. Water jacket. From my experiences with many water jackets, I have found that the one from 2coolcomputer does a decent job. They are sold for $25. Though they are not the top of the line, their pricing is good enough for the job you want to do. There are other waterjackets out there that are made of different material, construction and size. However, after testing a few out myself, the differences between all the waterjackets are minimal (within a few degrees C). The top of the line is probably becooling's copper waterjacket. However, this is expensive (over $35) but gives only about 2-4C better cooling than the cheapest 2coolcomputer's jacket.
2. Water radiator. You need a decent size one. I have 2 12inx5.5inx1in radiator. Again don't bother buying these from the vendors whose presence we have come across in this forum. Instead, head over to northern auto parts at naparts.com. Look in their catalog for transmission cooler. They sell these for $25. These are being sold be computer cooling vendors for around $35 or more. Yes, exactly the same one just at least $10 more. Greed at its best eh?
3. Water pump. Now you can get a decent water pump for around $20 at walmart or home depot. I think trinity sells a good pump but I don't know whether the price of the pump is still competitive or trinity has increased the price due to demand.
4. panaflo fans. You will need about 2 120mm panaflo fans. These are quiet to the point of inaudible while giving a decent air flow (66cfm). You can buy these at jameco.com. Again go to their catalog and look for page 65 of the catalog. It is under panaflo. Jameco used to sell these for $8.95 but since they noticed so many of us overclockers buying these fans, greed's bait got them and they increased the price to $10.50 or so (based on the latest catalog they sent me). I wish I have a few extra that I can sell to you guys for cheap $8.95 since I hate greedy pigs. However, $10.50 is still much better than some vendor's price of $15. Don't get suckered in, those fans are exactly the same price as Jameco's. I would not be amazed to find those vendors getting their supply from jameco themselves.
5. Tubings. Go to any hardware store or homedepot. These go for about $.20 per foot so again, don't buy from the vendors who sells them for $1.00 per foot. Major rip-off.
6. Water reservoir. Go to walmart and get a cooler for $8 or go to homedepot and get a electrical junction box. You can get the 4inx4in junction box that most vendors sell or go bigger and get a 7inx7in. The former costs around $5-7 and the later costs around $10-11.
Once you get all the parts, just plug them in. By then, if you need help, email me or pose your questions here. I am sure there are others more than willing to help.
So, all the parts should cost you around $100. That will be all that you will need. The connectors for the tubings will cost around $3. So, for $103, you should have a very good water cooler. That is the same parts that overclockerhideout is selling for $165 with a peltier. For an extra $25, to make it $125-130, you will have exactly the same system as overclockershideout with the exception that your fans will be larger, quieter, and stronger than the tiny 80mm fans.
However, the cost is still steep. So, my advice would be to go for a peltier with good aircooling for now. For $50, you probably can get the same performance.