Buying a computer system/computer with windows 8 that suits my needs
I'd like to purchase a new laptop with windows 8 on it, and replace my old laptop.
I generally use my laptop to surf the internet, watch movies, web development and sometimes use Photoshop. I do not play high-graphic video games.
What sort of computer would fit my needs? ( in terms of memory, ram, processor etc). I want to avoid paying more for additional features ( since I noticed that a 4 GB RAM laptop is way more expensive than a 2 GB RAM, but why would I need 4 GB RAM ?)
The majority of your usage scenarios are fairly low-demand, except for Photoshop, which is a very demanding application (it requires a powerful processor, and can require substantial amounts of memory and disk space as well, dependent on the complexity of your work). I'm curious, however, where you're getting the assertion that "a 4GB RAM laptop is way more expensive than a 2GB RAM" - 2GB of memory is an incredibly small load-out for a modern machine (in other words, I would avoid such a thing).
For example, looking at the Dell website, all of their entry-level offerings begin with 4GB of memory, and scale up considerably from there:
(I'm not aware of many offerings that will drop below $350 and still produce a brand-new, Windows-based, full-sized laptop from a reputable manufacturer; some non-Windows netbooks and Chromebooks will beat that pricing, but are entirely different animals)
In general I would not suggest a machine with less than 4GB of memory - Windows Vista, Windows 7, and Windows 8 all make extensive use of system memory, and so do many modern applications (like Photoshop, Internet Explorer, or Microsoft Office). There is no reason to purchase a modern system that is under-specified and under-equipped for modern software. Regarding how much memory you "need" - it's variable; memory does not make the system faster (per se), it simply allows the computer to have more applications open in memory (as opposed to paging file on the hard disk (which is very slow)), which can improve responsiveness or performance for applications that use a large amount of memory. Photoshop is a prime example of this - if Photoshop is forced to rely on paging file (or "scratch disk" as its documentation will refer to it), performance will suffer considerably, whereas if it can work from system memory, it is much less limited (as faster CPU will absolutely help as well). 4GB is a good starting-point for the kinds of applications you've mentioned, however if you're regularly working with very large projects in Photoshop, you may want to consider additional memory and a more robust processor (and remember - RAM is cheap, and processing power is generally not far behind). That having been said, unless you're dealing with truly massive projects (heavy multimedia content, often including HD video or audio), more than 8-12GB of memory will likely be of little benefit to you.
Something like this would be reasonable starting off point:
(they have other options, the primary difference will be screen size - other options (like memory, hard-disk, etc) are customizable before you order).
The inclusion of Windows 7 should not be a problem - it is just as competent as Windows 8 for conventional PC use; Windows 8's primary advantage is with tablet and touch-screen devices, and in many cases users report better overall functionality with Windows 7 for more conventional ("keyboard and mouse") usage.
Dell is not the only option, of course; Hewlett-Packard and Apple also make quality equipment. For your usage, Apple would be perfectly suitable (the primary "deterrent" for choosing Apple is if you wish to play games) - Photoshop will run just fine under OS X, and everything else is easily handled by equivalent applications (e.g. Safari in place of Internet Explorer). It isn't Windows, but Windows isn't absolutely required for your listed applications. The MacBook Air would likely be a reasonable choice as a starting-off point, unless you specifically want to spend more on the "Pro" model - it would certainly improve performance for high-demand Photoshop usage, but for everything else it would be overkill.
From HP, this system looks to be a good value overall:
(it offers more power than the Dell mentioned above, and the MacBook Air, and prices out in-betwixt them).
If you have further questions, feel free to ask.