 MaJOR tourism projects in the Highlands and Islands are in line for an GBP18 million cash boost from the European Regional Development Fund.  a new visitor centre for the chambered tomb of Maeshowe on Orkney and the Highlanders Museum Redevelopment Project near Inverness, which last year was backed by actor Hugh Grant, have received cash from the European fund, it was revealed yesterday.  Roads, ports and other infrastructure projects have also been awarded grants through the scheme, designed to regenerate areas suffering economic hardship.  Ian Johnstone, chairman of Orkney Island Council's development and regeneration committee, said the Maeshowe investment was welcome for such an important historic site.  Currently, the attraction's visitors' centre requires tourists to cross a main road and has very limited access.  The new project will provide access, education and community facilities on the mainland of Orkney.  Mr Johnstone said: "The site has struggled for a while and there were safety implications. This will make the whole experience better, and I think the new centre will help attract visitors."  Maeshowe will receive GBP1.14m, while the Highlanders museum project will benefit from GBP924,000.  The  