Thank you to Joe and Lee for replying with advice.
Since my original posting I've been persevering with the NAV menu and have learned a lot more about it. I finally managed to complete the 'Creating a Skin' part of the 'Building a Website' tutorial series, and I thought I'd post my findings here in case it helps someone else who may be struggling.
Of course, I'm still quite new to DotNetNuke so apologies if I've misunderstood something, or if there is a better way to achieve the desired result, unknown to me. Anyway, here are some thoughts...
1. It's possible to change the ProviderName in skin.xml - when I copied this from the DNN 4.8.2 DNN-Blue skin into the VortexMusic project (following Lee's tutorial) the ProviderName was set to 'DNNMenuNavigationProvider'. However, if you study the DotNetNuke Navigation WebControls
document (follow the 'Documents' link on http://webcontrols.dotnetnuke.com/DNNMenu.aspx) and scroll down to the table that begins around page 13 (actual page 17 in the pdf) and find the final 4 columns of ticks; the first column applies to 'SolpartMenuNavigationProvider' and the second column to 'DNNMenuNavigationProvider'. So out of curiosity I tried changing the ProviderName in skin.xml to SolpartMenuNavigationProvider and, after installing the skin, the menus seem to work but to be formatted differently - presumably as the Solpart Menu, though I have no knowledge yet of the way that this works. Being keen to get the NAV menu to work, I didn't explore this option further.
2. Its worth also noting that (on the second page of the above table), the CSSContainerRoot does not seem to be supported (no tick) for the DNNMenuNavigationProvider (as is also the case for CSSBreak), so you might as well comment out the corresponding styles (main_dnnmenu_container and main_dnnmenu_break respectively) in skin.css if you are using the DNNMenuNavigationProvider. I did verify that the CSSContainerRoot style was picked up when I changed the provider to the SolPart option, which seems to bear out the information in the document. As a result of the CSSContainerRoot not being available with the NAV menu, I had to apply the 'gradient_menu_vertical.jpg' background-image and associated styles to the .menupane style instead of the container style as suggested in Lee's tutorial video.
3. I could not find a way to limit the height of the menu container to 100px using styles alone. I resorted to creating a table within the leftpane TD element (menupane in the tutorial) and setting its TR height to 100. This seemed to work successfully. I placed a TD element within this TR and gave it the menupane style. The [NAV] token was placed as text in this TD element.
4. Put styles for the main menu text items under the .main_dnnmenu_rootitem style, for sub-menu items under main_dnnmenu_item and put styles for mouseover events under the .main_dnnmenu_itemhover style.
5. Where Lee's tutorial mentions SkinItem styles for the SolPart menu, substitute the word 'SkinObject' for 'SkinItem' when using the NAV menu.
I think this covers most of the differences. Apologies of I've missed anything out.
Now I'll have a go at learning about Containers...
Cheers,
Steve