Please, don't use an LM324 if you want to do precision measurements.  

Your opamp has a gain of 5, but you're not using that: Your output is the inverting input, where you have the same signal as the non-inverting, so that's gain x 1.  

The best choice would be an instrumentation amplifier, where you connect the cable's ends to the two inputs. Use a series resistor to ground to create an offset, because InAmps can't go to the rails (at least the 3-opamp types can't). You can use that resistor as a sense resistor for the current source:  



\$V_{IN}\$ sets the current of the current source: 100 mA/V. Suppose the cable's resistance is 5 &Omega;, then the InAmp will see a 500 mV difference on its input. A gain of 10 (gain resistor isn't shown; CircuitLab doesn't have a symbol for InAmps) will give you 5 V out, or 1 V/&Omega;. By changing \$V_{IN}\$ you can change the total gain. Note that Q1 may need a heatsink, especially if Vcc is rather high.  

 

If you expect high resistances you can make a resistor divider with 1 precision resistor to Vref, and one to ground:



The voltage across the cable will be

\$ V_{CABLE} = \dfrac{R_{CABLE}}{R_{CABLE} + 2 R} V_{REF} \$

but if \$R_{CABLE}\$ &lt;&lt; \$2 R\$ the voltage may be too low for an accurate measurement. A low value for \$R\$ helps, but will draw much current.

The MCP6N11 has Rail-to-Rail output and exists in different types for different gains, among which one for a gain of minimum 100.

edit
markrages comments that we don't need an InAmp, and he's right. Here's the solution with a differential amplifier using an opamp:  



The gain is determined by R1 through R4, and if R1 = R3 and R2 = R4 will be   

\$ G = \dfrac{R2}{R1}\$

An InAmp will give you more precision though, and it won't cost you an arm and a leg, so why not?

Measuring Resistance of a Wire With an ADC
I have a recently bought a NAS and am in the process of transferring my photo collection onto it. I probably have over 300GB of pictures (many in various RAW formats). At the moment these are just organized in “old fashioned” file structures but I have am hoping to improve this to a some sort of cross referenced tagging system. So far though I am running into a few problems and any help would be appreciated. I have tried using the following software:


Windows photo gallery - and this appears to rapidly retrieve photos from the NAS based on chose tag words. The main down side that I have found so far is that the windows camera codec does not yet support my S95 RAW files and so they are not visible. 
Picasa – this looks as though it might work well on a local drive (and certainly get good reviews) but I am finding it very slow when scanning the photo library on the NAS (even when left for a number of hours the scan in only approx. 5% complete!). I can live with a bit of a delay when using the NAS but this is unworkable - am I getting something wrong?
Various other photo viewers - Although they allow me to see my RAW files do not appear to support tagging and the development of a cross referenced library. 


I am also considering looking at getting Lightroom but don’t want to shell out the money only to find it is as slow as Picasa.

Finally, my ideal would be to have different layers of tags so for example I could tag all my pictures from the “Lake District” but then also have the option of sub dividing within this category based on the valley etc. Without different levels of tagging I risk winding up with an unwieldy list of tag words. I do not know if this is possible/normal but if anyone has any points about what software packages support this arrangement that would also be appreciated. 
