According to HP's specs found here http://h20000.www2.hp.com/bizsupport/TechSupport/Docume... your motherboard is micro-ATX form factor. I will highly advise against attempting to use a full ATX board in that chassis.
I might suggest the ASRock G41C-GS but I am unaware of any socket 775 CPU/mobo combo that will run ram natively at 1600MHz - the ram should work but will likely max out at 1333 unless overclocked.
Hope it helps
overall speed pereformance and to have more ram, as i have just realised that my motherboard only supports upto 4gb if im correct, and as i have 8gb theres 4 useless gb's. i would like it to not be green if possible as i have a white mars cit case that is part see through. i was hoping to have a nicer looking pc rather than the bog standard boring green.
One more thing to consider here is that a change of motherboard will require a new operating system since your Windows license through HP is for that 'system' with motherboard intact. Virually everything within a computer can be changed out without worrying about a new OS license, the motherboard is the exception. I think the ASRock board should work unless there are specific features you are looking for that are not there. Here is a list of your options as presented by Amazon http://www.amazon.co.uk/s/ref=nb_sb_noss?url=search-ali...