Currently I have Celeron 2.2ghz computer without even weak dedicated video card and really slow hdd. I can even work in After Effects and 3ds Max/maya on this machine, but it's very slow. Espetially in Lightroom, it's a pian to use it.
It's notebook, so I can't swap anything
The work your doing requires a open powerful workstation tower where you can add more RAM and swap out the video card for a newer more powerful one and have unlimited cooling and power.
This rules out the Mac Mini (a laptop in a box basically) and any laptop from just about any vendor, except perhaps from Sager then your opening it up and cleaning the cooling fins often of dust bunnies. (and it's really hot)
Your in the same catagory as a 3D gamer because you use Maya you need powerful 3D graphics and being able to upgrade the video card annually or bi-annually, all your 2D photo work will also improve with a powerful 3D tower/workstation.
Any video processing work would benefit from having more CPU cores to break the large job up into portions and send them to each core to work in parallel.
So basically what you require is a tower with many core processors AND a way to upgrade the graphics card often to get the latest 3D performance.
Unfortuntly you not going to find what you need on a Apple. Sure the MacPro has many core cpu's which video pro's like, but the problem is there isn't many 3D video graphic card upgrade options open for the MacPro (3x the price and 2x less performance) thus this is going to severly hamper your 3D rendering upgradability (and your wallet).
Also Apple upgrades OS X annually now, then drops support for older OS X versions requiring one to upgrade hardware (and software) much more rapidly than on Windows. Windows 7 will last until 2020, so you have less software headaches with paid upgrades etc with Windows. Your machine will stay the way it is on Windows, not on OS X which is undergoing radical and constant change. 😟
See this. https://discussions.apple.com/docs/DOC-4881
Apple is moving rapidly away from the professional market for their hardware anyway, basically only wants to cater to consumers with smaller devices. (as proof of the iPhone and iPad sales successes)
http://arstechnica.com/apple/2012/01/video-pros-apple-needs-to-acknowledge-the-p ro-industry-and-fast/
There is a free program called Cinebench, and what it does is it tests the CPU and Graphics performance of hardware for video pros and 3D gamers, which your a combination of both.
So you need the best CPU performance and the best GPU performance and this chart clearly shows which hardware you should buy + combined with Windows 7, a powerful machine for the next 7 years or more offline.
http://www.cbscores.com/index.php?sort=ogl&order=desc
So it's obvious you need a Win 7 tower, with many CPU cores and a powerful power supply and latest sockets on the motherboard to upgrade the newer video cards with.
You can use these charts here to find what your looking for in hardware.
http://www.cpubenchmark.net/high_end_cpus.html
http://www.videocardbenchmark.net/high_end_gpus.html
Now it's just a matter of finding a PC vendor that will either have the machine pre-built, or will build to suit.
If your in the US, Tiger Direct is known to build PC's to order and have pre-built 3D gaming systems, thus they can hold your hand and provide a warranty, a physical store to bring the machine in and advice.
Also a lot of local PC repair shops could likely set you up on a sweet system with a lot of power and performance.
Windows 7 isn't bad on a DECENT monitor, it's quite lovely on my 17" MacBook Pro here (yes Mac's can run Windows), the problem is your present machine is outdated and cheap consumer PC's have cheap monitors.
So if you get a high pixel per square inch monitor, Windows will look just as lovely as OS X on it with high pixel res photo's etc.
I know a Mac sounds like the answer to your prayers, but you'll soon realize it's not for what YOU need to do on the machine. The lack of software selection is pitiful, not only that a lot of Mac users will have to run Windows for some other piece of software eventually.
A Mac isn't for everyone and I rather be honest with you than lie just to trick you into buying a Mac, since your already used to Windows.
You can certainly buy a Mac or a iPad for other uses, but for what you require a Windows 7 workstation tower is clearly the best choice.