The A+ tests as stated are in two parts - Hardware and OS. You need a lot more than "a basic understanding of hardware" if you want to do well on the tests. First of all, one of the tests, and IMO the hardest one, is entirely OS related, so obviously any hardware knowledge is going to worthless for that purpose.

How easy/hard the tests are depend entirely on your current skillset and experience. If you have years of practical experience with computers, but you can't remember common IRQ's or what DB25 is you might scrape by, but the cert. does test for this kind of knowledge. Perhaps it's 'busy work', or something you can just look up, but IMO this is really 'grassroots' knowledge that you should at least touch on.

The OS tests focus a lot on NT kernel boot processes and priveleges, basic administration tasks, etc. I do not believe Win98 is even part of the test anymore, I had no questions on it.

Liek I said the difficulty the test will pose depends on your current level of expertise. If you are a total newb then a good class with hands-on practice would be a good idea. Otherwise you can most likely pick up a good book (try Mike Meyer's) and just brush up. I used Meyer's book and took both tests back to back, was out of there with my cert in about 30 minutes and passed with flying colors, so I highly recommend his books.