Question about compaq presario memory

I have a Compaq Presario 5716 which is a pretty old computer believe it was made around 1999. I have been using a newer alot faster dell for the past year but since I just moved I am back to using my old compaq. I have formatted several times to keep my hard drive clean and I know how to keep spyware off my system. Anyways I have been thinking about upgrading to more ram to see if it can help speed this old computer up. I was checking several websites and the cheapest I could find for 128mb was around $30 but I know that I can find the same memory for alot cheaper on ebay. My main question is that as I was looking over those websites a few of them said that Compaq Presarios use a "special kind of memory" and that if you buy cheaper memory it may not work with my computer. I took this to mean that if you dont know the difference between sdram or ddr and the difference between pc100, pc133 etc. to just buy what they tell you will be 100% compadible with your system. I do know exactly what type of memory I need and I am just wondering if it really makes a difference if I buy the specific kind the website tells me I need to. I figure that I should be all good if I just buy 128mb sd pc-100 with whatever brand name from ebay for alot cheaper. So am I thinking about this wrong? Do these compaqs really need a specific kind of memory? Also would it even be worth the money to upgrade more specfically would it make a noteable difference in overall speed? I have a p3 400mhz I believe so I dont think the processor is extremley outdated. Also if it helps I will list my computer specs below. Thanks for taking the time to read my post!

Compaq Presario 5716
p3 around 400mhz
14gb hd
96mb ram
3 memory sockets (2 used)
memory expandable up to 384mb
not sure of bus speed off the top of my head could find it if needed.

If I forgot anything in specs that will help please let me know. Thanks again

 

I would suggest www.crucial.com

 

Well I had already checked out crucial.com before I posted my original message and it was among those sites that I mentioned that charge alot more for what I can find on ebay for alot less. Here is the exact message that crucial.com gives me. This is also almost the same message all the other sites give also.

Important information about your computer
Your system only supports modules made with a specific type of chips. While you might find what appears to be the exact same memory for a lower price elsewhere, the cheaper memory might not work in your system. The Crucial Memory Selector only selects memory that is 100% guaranteed compatible with your system or we'll give you your money back! Learn more about chip density, memory prices, and compatibility here.

Now as I said in my original I somewhat understand the specs between different types of ram. So what I am trying to figure out is if I can use ram that is the same type in this case I would be using 128mb pc100 sdram more specifically making sure I buy non ecc ram with unbufferd dimm. Here is an example listing on ebay

128 mb
PC 100 100mhz
Non ECC
Tested and guaranteed
168 pin
Shipped in crush-proof boxes
VERY Compatible with DELL,COMPAQ, HP, TOSHIBA ,and more

Now to me that looks like it would work in my computer and if it did then I would be spending a whole lot less on memory. So what I am trying to figure out is if the specs need to match up exactly such as this ram being 16x64 cl2 or if as long as the ram matches up in being the same kind that my computer uses if it will work?

 

Here is another example from ebay. Again this appears that it would work and it is much cheaper.

These are two matching sticks of 128mb PC100 SDRAM (256mb total). This memory is in mint condition and is guaranteed against DOA.

Infineon

HYS64V16220GU-8

128mb, 100MHz, CL2

PC100

Unbuffered

Non-ECC

Double-sided (16 chips)