Few! managed to sort this out after a bit of head scratching.
By default xcart doesn't parse smarty within language variables. You can turn on the option to parse smarty in static pages in the admin>static pages but for some reason not language variables.
Anyhow, I did a search for ImagesDir in the languages and low and behold:
txt_vbv_admin_note
uses <img src="{{ImagesDir}}/vbv_pure_logo.gif" alt="" />
I searched for this string and it is in a few files along with the smarty code:
{$lng.txt_vbv_admin_note|substitute:"ImagesDir":$I magesDir}
So just go to skin1/customer/main/welcome.tpl and change:
{$lng.txt_welcome}
to
{$lng.txt_welcome|substitute:"ImagesDir":$ImagesDi r}
(without the spaces - not sure why these are coming up?)
then in your welcome_txt variable use {{ImagesDir}} in place of skin1/images/
I am not sure if there are any security issues but I am sure one of the guru's can answer this.