Hi Brad
Too bad about your computer, but you did say it was 6 or 7 yrs old? Most die sooner. Including macs.
The easiest way to make your decision is with the $ you are willing to spend. If your main use is internet and business accounting, you don't need an expensive computer. Under $500 will suit you fine. Check Future Shop sale flyers and you can get a capable computer in that range. If you want to go the Mac route, you do not have to spend $2k. A mac mini goes for about $600. Add a monitor for $150 -$250 and a mouse and keyboard and you're in business. It's not as clean looking as those computer built into the monitor versions, but it's still a mac with the lion op system and I'll bet the repair bills on those monitor/computer all in one units will be high. The salesman that told you the PC will last you 4-5 yrs and the mac 7-9 yrs is full of #$%^& in my opinion. In 5 years both systems will be very slow when compared with new systems of the day. How long you keep your computer will depend on how high a performance demand you put on it. Electronic failure will hit both types of system equally. The chips come from the same factories.
I've never met you, but, my impression from reading your posts is you would be happiest with a new PC type computer. The mac is a great computer, but there is also a learning curve with a new system. Do you want to spend time learning Lion or Snow Leopard(Mac OS) or just get back to surfing?
I'll be buying a new computer soon and it may be a Mac mini. Not because I have any problem with Windows PCs, its just fun to screw around with different electronic stuff.