I am going to try and offer my advice on buying a new laptop because there is so much choice in the market. Should you go for budget or brand name? AMD or Intel?
There are several types of laptop processor technologies available, including the new and very good Intel Centrino Duo. This technology is basically the same as the Centrino (mobile processor, Intel motherboard and integrated Intel Wireless) but includes the new dual-core or quad-core technology. This means that your computer can do more than one task at a time much quicker. In tests and the real world, this performs extremely well and is highly recommended. The new Intel Core 2 Duo (or very new Intel Core 2 Quad Mobile) are very good at multi-tasking as well as power-saving, giving you longer mobile battery life. The majority of these new processors support 64-bit operating systems. AMD continue to go with their Turion x2, a 64-bit dual-core mobile processor, that is very similar to the offering from Intel. This is also doing nicely and is quite future proof. I would personally buy Intel because they seem to be producing some really top quality processors. When looking to buy a processor, the clock speed is no longer the single most important thing. Processor speed along with bus speed and L2 Cache should also be taken into account when rating a processors power.
Should you buy a budget laptop or spend a bit more? From personal experience, the brand-name laptops are always better. They have better build-quality, warranties and support. They do not necissarily offer the same good specifications but you will be pleased with the build-quality and support offered by brand-name manufacturers. I purchased a laptop manufactured by a small company and the specification was, and still is, extremely good, but it does suffer from build quality and the design is quite poor and dull.
You should try and get as much RAM as you can. Windows Vista is very taxing on your computer, making 2048MB or more of RAM essential. Microsoft say that 512MB will suffice but you will suffer incredibly. On the Windows Vista note, it is important not to get confused between all of the different versions, but either go with Home Premium or Business. Basic is useless and Ultimate is a rip off! When choosing a laptop with 4096MB of RAM (4GB) you should be careful with the choice of operating system. Due to the physical addressing of memory space in 32-bit operating systems, they simply cannot see 4GB of RAM, making anything above 3.25GB useless. If you have 4GB of RAM, you really need to be using a 64-bit operating system to make any use of it. Beware though, 64-bit operating systems can have driver support problems (getting much better though) so check with your system manufacturer to see if they offer 64-bit drivers for your hardware if you plan on upgrading (if you buy the laptop with 64-bit pre-installed then you do not need to worry!).
Most new laptops have built-in Wireless networking capabilities. This does require you to have a router at home. If you do not at the moment, I cannot recommend it highly enough but if you're still unsure get a laptop with it anyway to future-proof yourself.
Most laptops have the new generation bright screens. Sony call them "X-Bright" and HP call them "BrightView" but they are basically the same technology from a third-party company. Get the biggest screen you can because then you will benefit in the future from High-Definition video. Some of the latest HP Pavilion laptops have 17" High Definition screens and they look absolutly beautiful. But remember, if portability is key for you, look at the overall dimensions and weight of the machine and try to balance them against screen size. Some chassis designs incorporate a larger screen into similar size chassis as smaller screened laptops.
So, why buy a laptop against a desktop? Well I would hope that the answer was obvious. There is no longer much difference in price, they are portable (surf the Internet wirelessly anywhere in your home with a WLAN), they look much nicer and are just as good (if not better) than a desktop. If you're limited to space, a laptop is the obvious choice.