IMAC running really slow!

I have about a 6 yr old imac which use to be flawless but recently is running terribly. I have read a few things that said it could be my macs memory. I looked at the activity monitor and realized I only have 1gb of memory and that only 12mb are free, 229mb inactive, 300 mb wired, and 475 active. I really dont know too much as far as technical issues are concerned which is why i am here, but it seems to me like this would be the problem?? Anyway, if anyone has any ideas on if i am right or wrong and what else it could possibly be please help! Also, if the memory is my problem, any suggestions on what a good 4gb memory would be and how much for it and install? Thanks for any help, I will check back often.

Hi could you please post your mac specs (year aswell if you know it), we can then help further in letting you know how much RAM your machine can take.
As for if it isn't your RAM, it could be your HDD is failing on you.

Cheers
- Simon

I believe i bought this imac in 2006. And yes, I have read also that it could be the hard drive but just hate to do anything and spend money on the wrong thing....here are the specs:

Model Name: iMac
Model Identifier: iMac5,1
Processor Name: Intel Core 2 Duo
Processor Speed: 2.16 GHz
Number Of Processors: 1
Total Number Of Cores: 2
L2 Cache: 4 MB
Memory: 1 GB
Bus Speed: 667 MHz
Boot ROM Version: IM51.0090.B09
SMC Version (system): 1.9f4
Serial Number (system): W86391X9VUV
Hardware UUID: 00000000-0000-1000-8000-0016CBA06E63

If you need any other info just let me know..

Here is the upgradability (if thats a word

Latest release of Mac OS X
3.0 GB (4.0 GB can be installed, only 3.0 GB will be addressed)
2 - 200-pin PC2-5300 (667MHz) DDR2 SO-DIMM

Hope this helps

- Simon

is that ram you are referring to? If so, there are 2 things i need to buy and install? Im sorry I just dont know too much about hardware. Also, how much would this run me to buy and have installed.

Hiya, ok so it is RAM and "3.0 GB (4.0 GB can be installed, only 3.0 GB will be addressed)" means that you can install 2 x 2GB sticks making it 4GB, however the hardware in the iMac means that it will only ever address 3 out of the 4GB of RAM installed.
"2 - 200-pin PC2-5300 (667MHz) DDR2 SO-DIMM" is the RAM type, translation = 2 x 200pin 'PC2-5300' DDR2 SO-DIMM = 2 sticks of 200 pin etc.

Here's some info on where and how much... if you need US or other prices let me know.

Crucial 4 GB : 2 x 2 GB Memory - SO DIMM 200-pin - 667 MHz ( PC2-5300 )

Hope this helps

- Simon

And how full is the hard drive? Over 85% capacity will start to slow down your iMac.

i have about 130 gb left on my 250 drive. Is there any clear way to distinguish whether the problem is lack of ram or hard drive is failing? I hate to buy one and install it and find out its the other that needs fixing and then i wasted my money.