Welcome to Aximsite, Spiff. You will find this site is a treasure trove of valuable information. Go exploring with the search feature to find out much from those with far more experience than I -- here's my 2-cents worth.
Viruses - From what I've read here, many of us do not use PDA antivirus, although a few products are avialable. The importance of having one on your PDA depends on how you surf. I connect to the internet only from behind a firewall with built-in anti-virus, which is why I don't use anti-virus directly on my Axim. PDA's dont' seem to be as big a target for viruses as some other MicroSoft products. If you use your Axim for work, check with your IT department regarding their policies.
Movies - search out Core's TCPMP (
http://tcpmp.corecodec.org/), and take a look at SPB's Mobile DVD (
http://www.spbsoftwarehouse.com/products/mobiledvd/?en).
Sufficiency of storage obviously depends on what you store. I get by wonderfully with a single 512 SD, but I don't store movies.
Install/load - many software packages come with ability to install either through ActiveSync (typically ending in "exe") or directly from your PDA (typically ending in "cab"). You can download cab's directly to your Axim while surfing, and double click on them to install. Sometimes exe's offer some more features than cab's: read carefully
I've had my x50v for two years, and I'm still learning plenty. Don't rush into buying software; if you find something in which you're interested, do search this site for others' experience with it. There's lot of freeware out there; remember you get what you pay for (although several freeware's are fabulous).
Again, welcome to aximsite, Spiff.