Replacing old monitor in grandpa's pc

A 1920x1080 resolution, a response time of 5ms or better and LED backlighting. Thats pretty much all you have to worry about.

Something like this would be good.
ASUS VS248H-P Black 24". $200 ($20 rebate, 20% promo code)
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

how are so sure that the old intel gma 915 would support that resolution, also it only has a vga port!

The monitor has a VGA port, for some reson they call it D-SUB on spec sheets.

I cant be unless you can provide a specific CPU that the system is using. But you would have to go quite a ways back before you can find any graphics that couldnt support 1920x1080. The VGA connection itself is capable of outputting that resolution.
Plus according to this.
http://www.intel.com/products/chipsets/gma900/index.htm
The GMA900 series is capable of supporting 16:9 ratio resolutions, which 1920x1080 is.

And if the system cant, then it will just display the highest resolution it can. So you get the best image possible and you have a decent quality monitor that can be used on a different rig without issue.

Surprisingly this info is hard to find.

I cant prove that it will support 1920x1080, cant find anything that says it cant. I guess you'l just have to roll the dice on this.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...
the asus should for it price give your old dad the same look and feel of the crt on an lcd screen and not break the bank. also the monitor has newer video port if dad pc ever kicks the bucket or someone gives him a newer pc.
myself i would talk to the family and toss in some cash and build him a newer pc. you need to be able to run newer browsers one for safety the older ones can be hacked real easy and also a lot of the newer www content needs a newer browser to work.
a 4 gig machine with windows 7 and an two core amd or two core g cpu and a 40.00 mb and 500g drive using onboard video will last dear old dad a long long time. the plus side he love the newer machine as it be a lot faster.