convert txt file to csv seperated with tabs

Sorry people I'm new to Linux, and while I looked through the list of answered questions, I don't know enough to recognize if my question was answered. Or if I can adapt one of the answer to my particular little problem.

I get a text file of data from my boss, who learned to use computers one way; and he won't change. The data is almost a csv file, except the fields are all separated by a space characters rather then a comma or tab character. And the text fields of data include embedded spaces also.

Each field is either a number or is numbers and text, all fields are of varying lengths, and none are off-set with single or double quotes. The number fields predominate, and no text field is adjacent to any other text field. Rarely is an embedded number in a text field preceded or followed by a [space] character.

Unfortunately not every [space] character can just be replaced. Instead because, generally, field breaks come in the form of either [space][0-9] or [0-9][space], this is how I determine if a [space] character should be converted to a [tab] character or not. If the [space] character is beside a digit its to be converted to a [tab] character.

So using the Find/Replace function in Notepad for Windows, I search for a digit-space or a space-digit combination, converting that [space] character to a [tab] character. I have to do this ten times [0-9][space] and then ten more times [space][0-9]. I'm looking for a script to do this automatically.

Here is an example of the file I get. It contains four fields separated by [space] characters (first line). Each following line is one record, so the second line is the first record. Account is 2281, Units are 19, Description is Toshiba PX-1982GRSUB{, and finally the Delta field contains the 0:

Account Units Description Delta  
2281 19 Toshiba PX-1982GRSUB 0  
9618 200 HP MX19942-228b -25  
19246 4 CompuCom HD300g Hard Drive 4

So what I'm looking for is a script that will read the original file, convert the [space] characters that are field separators into characters and write it all to a new file. And I want the explanation -- so I don't keep asking the same questions over and over again.