Literally, 'the art/skill of living without legs'. Classical Latin has no real equivilent primary participial or gerundive forms for 'esse'. 'to be', although I believe that in Mediaeval Latin one could say 'ars essendi sine cruribus', which would be a more literal, if less elegant, translation of the phrase.

Other nearly synonymous Latin renderings would be 'ars exsistendi sine cruribus' ('the art/skill of existing/ without legs'), where 'exsistendi' comes very close to 'being' in its signfication, or else, more colloquially and neatly, 'ars sui habendi sine cruribus', 'the art/skill of keeping/maintaining onself without legs'. This last phrase refers to males; if you are female, you would say, 'ars sui habendae sine cruribus'.

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Note added at 8 hrs (2006-05-17 23:20:25 GMT)
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For the use of 'se habere' as virtually equivilent to 'to be such and such in some manner or other', cf. , e.g., Cicero, 'ad Atticum', 7.2.3: quamquam videbatur se non graviter habere, tamen sum sollicitus, "Although he didn't seem to be in a bad way, I was nonetheless upset"; Id., 'ad Atticum', 13.35.2: scire aveo quomodo res se habeat, "I'm eager to know how the situation is [i.r., stands]"; Tacitus, 'Annales', 14.51: cum ad visendum eum princeps venisset, aspectum eius aversatum sciscitanti hactenus respondisse: 'ego me bene habeo, "Whenever the prince had come to visit him, his face turned away in shame, [he is said] to have responded to the man previously investigating, "I am well [lit., "I keep myself well"]; Terence, Phormio, 820: "Laetus sum ut meae res sese habent, "I'm delighted how well my circumstances are", etc. 'Se habere' in CLASSICAL Latin, often in conjunction with 'res' as subject nominative, with an adverb or predicate adjective, or in an indirect question is a construction found in virtually every major writer and poet from Cato and Ennius to Tacitus and Juvenal, and beyond. It is a natural, colloquial way of saying that something or someone contiues to BE in a certain way, condition, position, circumstance, or the like, although those who prefer to render Latin too literally, at the expense of intrinsic meaning, don't seem to recognise what is obvious to most readers.

Admittedly, the suggested construction with the gerundive may not be precedented so far as this paraticular idiom Z(i.e., 'se habere') goes, but it likewise is quite natural, colloquial, and elegant (unless one deems Cicero's correspondence bad prose--an opinion which very few have espoused since Tiro published them after his patron's death.