Tools Needed: 
Welder (!)
Grinder with cutting and grinding discs
Electric drill & bits
Safety goggles, ear muffs, welding helmet etc
13 & 17mmsocket & spanner
Screwdriver
Lots of G clamps & molegrips                                       *more pics to be added soon*

Parts Needed: (depending on how bad yours is)
front valance panel
wheel well panel
2 front bumper mount panels 
2 wings front 
bumper
or pre-made front clip panel (petrol tank forward)

Time taken: A day/ easy weekend

This how to assumes you need to replace the whole front area either due to rust of a front-eng shunt  Take you time, measure & trial fit as often as possible so that it fits right 1st time.

Getting started
Before doing any welding always disconnect the battery.
Take the front wings and bumper off including the bumper irons & horn.
Next,  remove the petrol tank. To do this undo the 4 13mm bolts holding the tank to the 'boot' floor. Now remove the breather pipes if there are any attached. Next unscrew the clamp holding the flexi pipe from the tank to the pipe that goes through the body. Bung the bottom of this pipe (a pencil or screwdriver is a handy size) and lift the tank out. 

Finally, you'll need to remove the bonnet catch from the front valance. This will either unbolt or you may have to drill out some rivets. Don't disconnect the wire pull.

Modifying the replacement panel
If you are after a good finish with this panel you will first have to modify the replacement font clip. As pic one shows, they are for LHD cars so you need to cut an inspection hatch in the right hand side and make the square hole the correct semi-circle. To do this I cut the openings out of the original panel and welded them in (pic2).

The first cut
Before you attack it with a grinder, measure where the new panel comes to on the body, If at all possible, take less off the bug body and trim the new panel down to size. Measure from the A post to the front of the car, the petrol tank opening and the gaps between the middle from wing bolts. Use this mark as a guide when gutting the old panel off. A good idea is cut at least an inch below the marked line so that you have some to play with. If you don't need to put the whole panel in, trim it down to size, then mark up on the car.  Once you've marked up carefully cut off the old front clip, but leave some excess to be trimmed back later - it's much easier to trim it off than put it back on. Undo the 2 bolts holding the front clip to the top of the front beam (behind the washer bottle recess) and keep hold of the rubber block spacers.  It'll now look like:

Putting it all back on
Bolt the 2 mounting bolts into the top of the beam with the rubber blocks in their right place. Now, when you've double checked measurements etc, trim the panel back to the line you made for the cut off and clamp this in place. You want to butt weld the panel, so leave a gap about the width (*not depth or length*) of a hacksaw blade.  Fit the front wings to check the gaps between the bolt holes are correct and that the bottoms of the front wings are flush with the bottom of the valance. Refit the petrol tank too, to make sure the opening is big enough. Close the bonnet and check for the required length and that the sides gaps are good. With the pre-built clips you'll find this area will need work. I usually leave this 'till the panel is in place. 
Happy? tack it in place & recheck all measurements, fitments etc. 
Once that's ok, weld it all in slowly, taking care to avoid heat build up in the panels. Use a damp rag as a heat sink. 
As mentioned above it's quite likely the joining area at the top of the panel where the bonnet seal usually fits will probably not be a good join. To correct this, don't weld right up to the top of the side. Leave about 5 cam or so un-welded to give you flex. It might be necessary to cut a horizontal line under the curve to drop the panel down to meet the curve of the bug body. Take your time here and get it right, otherwise it will stand out a mile when it's done. Once that's ok, weld that in too

Finishing it off
Grind down your welds so they are invisible. Look behind where the wheel well joined the body and you'll see the panel curves around providing an excellent water trap. Fill this with seam sealer & paint over it to keep the water out

Bit of paint, put everything back together and go brew a cuppa